Move all lua related files to lua/ subfolder

Also remove the lexers sub directory from the Lua search path.
As a result we attempt to open fewer files during startup:

 $ strace -e open -o log ./vis +q config.h && wc -l log

In order to avoid having to modifiy all lexers which `require('lexer')`
we instead place a symlink in the top level directory.

 $ ./configure --disable-lua
 $ rm -rf lua

Should result in a source tree with most lua specifc functionality
removed.

1 files changed, 1634 insertions, 0 deletions

diff --git a/lua/lexers/lexer.lua b/lua/lexers/lexer.lua
new file mode 100644
index 0000000..b896344
--- /dev/null
+++ b/lua/lexers/lexer.lua
@@ -0,0 +1,1634 @@
+-- Copyright 2006-2016 Mitchell mitchell.att.foicica.com. See LICENSE.
+
+local M = {}
+
+--[=[ This comment is for LuaDoc.
+---
+-- Lexes Scintilla documents with Lua and LPeg.
+--
+-- ## Overview
+--
+-- Lexers highlight the syntax of source code. Scintilla (the editing component
+-- behind [Textadept][] and [SciTE][]) traditionally uses static, compiled C++
+-- lexers which are notoriously difficult to create and/or extend. On the other
+-- hand, Lua makes it easy to to rapidly create new lexers, extend existing
+-- ones, and embed lexers within one another. Lua lexers tend to be more
+-- readable than C++ lexers too.
+--
+-- Lexers are Parsing Expression Grammars, or PEGs, composed with the Lua
+-- [LPeg library][]. The following table comes from the LPeg documentation and
+-- summarizes all you need to know about constructing basic LPeg patterns. This
+-- module provides convenience functions for creating and working with other
+-- more advanced patterns and concepts.
+--
+-- Operator             | Description
+-- ---------------------|------------
+-- `lpeg.P(string)`     | Matches `string` literally.
+-- `lpeg.P(`_`n`_`)`    | Matches exactly _`n`_ characters.
+-- `lpeg.S(string)`     | Matches any character in set `string`.
+-- `lpeg.R("`_`xy`_`")` | Matches any character between range `x` and `y`.
+-- `patt^`_`n`_         | Matches at least _`n`_ repetitions of `patt`.
+-- `patt^-`_`n`_        | Matches at most _`n`_ repetitions of `patt`.
+-- `patt1 * patt2`      | Matches `patt1` followed by `patt2`.
+-- `patt1 + patt2`      | Matches `patt1` or `patt2` (ordered choice).
+-- `patt1 - patt2`      | Matches `patt1` if `patt2` does not match.
+-- `-patt`              | Equivalent to `("" - patt)`.
+-- `#patt`              | Matches `patt` but consumes no input.
+--
+-- The first part of this document deals with rapidly constructing a simple
+-- lexer. The next part deals with more advanced techniques, such as custom
+-- coloring and embedding lexers within one another. Following that is a
+-- discussion about code folding, or being able to tell Scintilla which code
+-- blocks are "foldable" (temporarily hideable from view). After that are
+-- instructions on how to use LPeg lexers with the aforementioned Textadept and
+-- SciTE editors. Finally there are comments on lexer performance and
+-- limitations.
+--
+-- [LPeg library]: http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html
+-- [Textadept]: http://foicica.com/textadept
+-- [SciTE]: http://scintilla.org/SciTE.html
+--
+-- ## Lexer Basics
+--
+-- The *lexers/* directory contains all lexers, including your new one. Before
+-- attempting to write one from scratch though, first determine if your
+-- programming language is similar to any of the 80+ languages supported. If so,
+-- you may be able to copy and modify that lexer, saving some time and effort.
+-- The filename of your lexer should be the name of your programming language in
+-- lower case followed by a *.lua* extension. For example, a new Lua lexer has
+-- the name *lua.lua*.
+--
+-- Note: Try to refrain from using one-character language names like "c", "d",
+-- or "r". For example, Scintillua uses "ansi_c", "dmd", and "rstats",
+-- respectively.
+--
+-- ### New Lexer Template
+--
+-- There is a *lexers/template.txt* file that contains a simple template for a
+-- new lexer. Feel free to use it, replacing the '?'s with the name of your
+-- lexer:
+--
+--     -- ? LPeg lexer.
+--
+--     local l = require('lexer')
+--     local token, word_match = l.token, l.word_match
+--     local P, R, S = lpeg.P, lpeg.R, lpeg.S
+--
+--     local M = {_NAME = '?'}
+--
+--     -- Whitespace.
+--     local ws = token(l.WHITESPACE, l.space^1)
+--
+--     M._rules = {
+--       {'whitespace', ws},
+--     }
+--
+--     M._tokenstyles = {
+--
+--     }
+--
+--     return M
+--
+-- The first 3 lines of code simply define often used convenience variables. The
+-- 5th and last lines define and return the lexer object Scintilla uses; they
+-- are very important and must be part of every lexer. The sixth line defines
+-- something called a "token", an essential building block of lexers. You will
+-- learn about tokens shortly. The rest of the code defines a set of grammar
+-- rules and token styles. You will learn about those later. Note, however, the
+-- `M.` prefix in front of `_rules` and `_tokenstyles`: not only do these tables
+-- belong to their respective lexers, but any non-local variables need the `M.`
+-- prefix too so-as not to affect Lua's global environment. All in all, this is
+-- a minimal, working lexer that you can build on.
+--
+-- ### Tokens
+--
+-- Take a moment to think about your programming language's structure. What kind
+-- of key elements does it have? In the template shown earlier, one predefined
+-- element all languages have is whitespace. Your language probably also has
+-- elements like comments, strings, and keywords. Lexers refer to these elements
+-- as "tokens". Tokens are the fundamental "building blocks" of lexers. Lexers
+-- break down source code into tokens for coloring, which results in the syntax
+-- highlighting familiar to you. It is up to you how specific your lexer is when
+-- it comes to tokens. Perhaps only distinguishing between keywords and
+-- identifiers is necessary, or maybe recognizing constants and built-in
+-- functions, methods, or libraries is desirable. The Lua lexer, for example,
+-- defines 11 tokens: whitespace, comments, strings, numbers, keywords, built-in
+-- functions, constants, built-in libraries, identifiers, labels, and operators.
+-- Even though constants, built-in functions, and built-in libraries are subsets
+-- of identifiers, Lua programmers find it helpful for the lexer to distinguish
+-- between them all. It is perfectly acceptable to just recognize keywords and
+-- identifiers.
+--
+-- In a lexer, tokens consist of a token name and an LPeg pattern that matches a
+-- sequence of characters recognized as an instance of that token. Create tokens
+-- using the [`lexer.token()`]() function. Let us examine the "whitespace" token
+-- defined in the template shown earlier:
+--
+--     local ws = token(l.WHITESPACE, l.space^1)
+--
+-- At first glance, the first argument does not appear to be a string name and
+-- the second argument does not appear to be an LPeg pattern. Perhaps you
+-- expected something like:
+--
+--     local ws = token('whitespace', S('\t\v\f\n\r ')^1)
+--
+-- The `lexer` (`l`) module actually provides a convenient list of common token
+-- names and common LPeg patterns for you to use. Token names include
+-- [`lexer.DEFAULT`](), [`lexer.WHITESPACE`](), [`lexer.COMMENT`](),
+-- [`lexer.STRING`](), [`lexer.NUMBER`](), [`lexer.KEYWORD`](),
+-- [`lexer.IDENTIFIER`](), [`lexer.OPERATOR`](), [`lexer.ERROR`](),
+-- [`lexer.PREPROCESSOR`](), [`lexer.CONSTANT`](), [`lexer.VARIABLE`](),
+-- [`lexer.FUNCTION`](), [`lexer.CLASS`](), [`lexer.TYPE`](), [`lexer.LABEL`](),
+-- [`lexer.REGEX`](), and [`lexer.EMBEDDED`](). Patterns include
+-- [`lexer.any`](), [`lexer.ascii`](), [`lexer.extend`](), [`lexer.alpha`](),
+-- [`lexer.digit`](), [`lexer.alnum`](), [`lexer.lower`](), [`lexer.upper`](),
+-- [`lexer.xdigit`](), [`lexer.cntrl`](), [`lexer.graph`](), [`lexer.print`](),
+-- [`lexer.punct`](), [`lexer.space`](), [`lexer.newline`](),
+-- [`lexer.nonnewline`](), [`lexer.nonnewline_esc`](), [`lexer.dec_num`](),
+-- [`lexer.hex_num`](), [`lexer.oct_num`](), [`lexer.integer`](),
+-- [`lexer.float`](), and [`lexer.word`](). You may use your own token names if
+-- none of the above fit your language, but an advantage to using predefined
+-- token names is that your lexer's tokens will inherit the universal syntax
+-- highlighting color theme used by your text editor.
+--
+-- #### Example Tokens
+--
+-- So, how might you define other tokens like comments, strings, and keywords?
+-- Here are some examples.
+--
+-- **Comments**
+--
+-- Line-style comments with a prefix character(s) are easy to express with LPeg:
+--
+--     local shell_comment = token(l.COMMENT, '#' * l.nonnewline^0)
+--     local c_line_comment = token(l.COMMENT, '//' * l.nonnewline_esc^0)
+--
+-- The comments above start with a '#' or "//" and go to the end of the line.
+-- The second comment recognizes the next line also as a comment if the current
+-- line ends with a '\' escape character.
+--
+-- C-style "block" comments with a start and end delimiter are also easy to
+-- express:
+--
+--     local c_comment = token(l.COMMENT, '/*' * (l.any - '*/')^0 * P('*/')^-1)
+--
+-- This comment starts with a "/\*" sequence and contains anything up to and
+-- including an ending "\*/" sequence. The ending "\*/" is optional so the lexer
+-- can recognize unfinished comments as comments and highlight them properly.
+--
+-- **Strings**
+--
+-- It is tempting to think that a string is not much different from the block
+-- comment shown above in that both have start and end delimiters:
+--
+--     local dq_str = '"' * (l.any - '"')^0 * P('"')^-1
+--     local sq_str = "'" * (l.any - "'")^0 * P("'")^-1
+--     local simple_string = token(l.STRING, dq_str + sq_str)
+--
+-- However, most programming languages allow escape sequences in strings such
+-- that a sequence like "\\"" in a double-quoted string indicates that the
+-- '"' is not the end of the string. The above token incorrectly matches
+-- such a string. Instead, use the [`lexer.delimited_range()`]() convenience
+-- function.
+--
+--     local dq_str = l.delimited_range('"')
+--     local sq_str = l.delimited_range("'")
+--     local string = token(l.STRING, dq_str + sq_str)
+--
+-- In this case, the lexer treats '\' as an escape character in a string
+-- sequence.
+--
+-- **Keywords**
+--
+-- Instead of matching _n_ keywords with _n_ `P('keyword_`_`n`_`')` ordered
+-- choices, use another convenience function: [`lexer.word_match()`](). It is
+-- much easier and more efficient to write word matches like:
+--
+--     local keyword = token(l.KEYWORD, l.word_match{
+--       'keyword_1', 'keyword_2', ..., 'keyword_n'
+--     })
+--
+--     local case_insensitive_keyword = token(l.KEYWORD, l.word_match({
+--       'KEYWORD_1', 'keyword_2', ..., 'KEYword_n'
+--     }, nil, true))
+--
+--     local hyphened_keyword = token(l.KEYWORD, l.word_match({
+--       'keyword-1', 'keyword-2', ..., 'keyword-n'
+--     }, '-'))
+--
+-- By default, characters considered to be in keywords are in the set of
+-- alphanumeric characters and underscores. The last token demonstrates how to
+-- allow '-' (hyphen) characters to be in keywords as well.
+--
+-- **Numbers**
+--
+-- Most programming languages have the same format for integer and float tokens,
+-- so it might be as simple as using a couple of predefined LPeg patterns:
+--
+--     local number = token(l.NUMBER, l.float + l.integer)
+--
+-- However, some languages allow postfix characters on integers.
+--
+--     local integer = P('-')^-1 * (l.dec_num * S('lL')^-1)
+--     local number = token(l.NUMBER, l.float + l.hex_num + integer)
+--
+-- Your language may need other tweaks, but it is up to you how fine-grained you
+-- want your highlighting to be. After all, you are not writing a compiler or
+-- interpreter!
+--
+-- ### Rules
+--
+-- Programming languages have grammars, which specify valid token structure. For
+-- example, comments usually cannot appear within a string. Grammars consist of
+-- rules, which are simply combinations of tokens. Recall from the lexer
+-- template the `_rules` table, which defines all the rules used by the lexer
+-- grammar:
+--
+--     M._rules = {
+--       {'whitespace', ws},
+--     }
+--
+-- Each entry in a lexer's `_rules` table consists of a rule name and its
+-- associated pattern. Rule names are completely arbitrary and serve only to
+-- identify and distinguish between different rules. Rule order is important: if
+-- text does not match the first rule, the lexer tries the second rule, and so
+-- on. This simple grammar says to match whitespace tokens under a rule named
+-- "whitespace".
+--
+-- To illustrate the importance of rule order, here is an example of a
+-- simplified Lua grammar:
+--
+--     M._rules = {
+--       {'whitespace', ws},
+--       {'keyword', keyword},
+--       {'identifier', identifier},
+--       {'string', string},
+--       {'comment', comment},
+--       {'number', number},
+--       {'label', label},
+--       {'operator', operator},
+--     }
+--
+-- Note how identifiers come after keywords. In Lua, as with most programming
+-- languages, the characters allowed in keywords and identifiers are in the same
+-- set (alphanumerics plus underscores). If the lexer specified the "identifier"
+-- rule before the "keyword" rule, all keywords would match identifiers and thus
+-- incorrectly highlight as identifiers instead of keywords. The same idea
+-- applies to function, constant, etc. tokens that you may want to distinguish
+-- between: their rules should come before identifiers.
+--
+-- So what about text that does not match any rules? For example in Lua, the '!'
+-- character is meaningless outside a string or comment. Normally the lexer
+-- skips over such text. If instead you want to highlight these "syntax errors",
+-- add an additional end rule:
+--
+--     M._rules = {
+--       {'whitespace', ws},
+--       {'error', token(l.ERROR, l.any)},
+--     }
+--
+-- This identifies and highlights any character not matched by an existing
+-- rule as an `lexer.ERROR` token.
+--
+-- Even though the rules defined in the examples above contain a single token,
+-- rules may consist of multiple tokens. For example, a rule for an HTML tag
+-- could consist of a tag token followed by an arbitrary number of attribute
+-- tokens, allowing the lexer to highlight all tokens separately. The rule might
+-- look something like this:
+--
+--     {'tag', tag_start * (ws * attributes)^0 * tag_end^-1}
+--
+-- Note however that lexers with complex rules like these are more prone to lose
+-- track of their state.
+--
+-- ### Summary
+--
+-- Lexers primarily consist of tokens and grammar rules. At your disposal are a
+-- number of convenience patterns and functions for rapidly creating a lexer. If
+-- you choose to use predefined token names for your tokens, you do not have to
+-- define how the lexer highlights them. The tokens will inherit the default
+-- syntax highlighting color theme your editor uses.
+--
+-- ## Advanced Techniques
+--
+-- ### Styles and Styling
+--
+-- The most basic form of syntax highlighting is assigning different colors to
+-- different tokens. Instead of highlighting with just colors, Scintilla allows
+-- for more rich highlighting, or "styling", with different fonts, font sizes,
+-- font attributes, and foreground and background colors, just to name a few.
+-- The unit of this rich highlighting is called a "style". Styles are simply
+-- strings of comma-separated property settings. By default, lexers associate
+-- predefined token names like `lexer.WHITESPACE`, `lexer.COMMENT`,
+-- `lexer.STRING`, etc. with particular styles as part of a universal color
+-- theme. These predefined styles include [`lexer.STYLE_CLASS`](),
+-- [`lexer.STYLE_COMMENT`](), [`lexer.STYLE_CONSTANT`](),
+-- [`lexer.STYLE_ERROR`](), [`lexer.STYLE_EMBEDDED`](),
+-- [`lexer.STYLE_FUNCTION`](), [`lexer.STYLE_IDENTIFIER`](),
+-- [`lexer.STYLE_KEYWORD`](), [`lexer.STYLE_LABEL`](), [`lexer.STYLE_NUMBER`](),
+-- [`lexer.STYLE_OPERATOR`](), [`lexer.STYLE_PREPROCESSOR`](),
+-- [`lexer.STYLE_REGEX`](), [`lexer.STYLE_STRING`](), [`lexer.STYLE_TYPE`](),
+-- [`lexer.STYLE_VARIABLE`](), and [`lexer.STYLE_WHITESPACE`](). Like with
+-- predefined token names and LPeg patterns, you may define your own styles. At
+-- their core, styles are just strings, so you may create new ones and/or modify
+-- existing ones. Each style consists of the following comma-separated settings:
+--
+-- Setting        | Description
+-- ---------------|------------
+-- font:_name_    | The name of the font the style uses.
+-- size:_int_     | The size of the font the style uses.
+-- [not]bold      | Whether or not the font face is bold.
+-- weight:_int_   | The weight or boldness of a font, between 1 and 999.
+-- [not]italics   | Whether or not the font face is italic.
+-- [not]underlined| Whether or not the font face is underlined.
+-- fore:_color_   | The foreground color of the font face.
+-- back:_color_   | The background color of the font face.
+-- [not]eolfilled | Does the background color extend to the end of the line?
+-- case:_char_    | The case of the font ('u': upper, 'l': lower, 'm': normal).
+-- [not]visible   | Whether or not the text is visible.
+-- [not]changeable| Whether the text is changeable or read-only.
+--
+-- Specify font colors in either "#RRGGBB" format, "0xBBGGRR" format, or the
+-- decimal equivalent of the latter. As with token names, LPeg patterns, and
+-- styles, there is a set of predefined color names, but they vary depending on
+-- the current color theme in use. Therefore, it is generally not a good idea to
+-- manually define colors within styles in your lexer since they might not fit
+-- into a user's chosen color theme. Try to refrain from even using predefined
+-- colors in a style because that color may be theme-specific. Instead, the best
+-- practice is to either use predefined styles or derive new color-agnostic
+-- styles from predefined ones. For example, Lua "longstring" tokens use the
+-- existing `lexer.STYLE_STRING` style instead of defining a new one.
+--
+-- #### Example Styles
+--
+-- Defining styles is pretty straightforward. An empty style that inherits the
+-- default theme settings is simply an empty string:
+--
+--     local style_nothing = ''
+--
+-- A similar style but with a bold font face looks like this:
+--
+--     local style_bold = 'bold'
+--
+-- If you want the same style, but also with an italic font face, define the new
+-- style in terms of the old one:
+--
+--     local style_bold_italic = style_bold..',italics'
+--
+-- This allows you to derive new styles from predefined ones without having to
+-- rewrite them. This operation leaves the old style unchanged. Thus if you
+-- had a "static variable" token whose style you wanted to base off of
+-- `lexer.STYLE_VARIABLE`, it would probably look like:
+--
+--     local style_static_var = l.STYLE_VARIABLE..',italics'
+--
+-- The color theme files in the *lexers/themes/* folder give more examples of
+-- style definitions.
+--
+-- ### Token Styles
+--
+-- Lexers use the `_tokenstyles` table to assign tokens to particular styles.
+-- Recall the token definition and `_tokenstyles` table from the lexer template:
+--
+--     local ws = token(l.WHITESPACE, l.space^1)
+--
+--     ...
+--
+--     M._tokenstyles = {
+--
+--     }
+--
+-- Why is a style not assigned to the `lexer.WHITESPACE` token? As mentioned
+-- earlier, lexers automatically associate tokens that use predefined token
+-- names with a particular style. Only tokens with custom token names need
+-- manual style associations. As an example, consider a custom whitespace token:
+--
+--     local ws = token('custom_whitespace', l.space^1)
+--
+-- Assigning a style to this token looks like:
+--
+--     M._tokenstyles = {
+--       custom_whitespace = l.STYLE_WHITESPACE
+--     }
+--
+-- Do not confuse token names with rule names. They are completely different
+-- entities. In the example above, the lexer assigns the "custom_whitespace"
+-- token the existing style for `WHITESPACE` tokens. If instead you want to
+-- color the background of whitespace a shade of grey, it might look like:
+--
+--     local custom_style = l.STYLE_WHITESPACE..',back:$(color.grey)'
+--     M._tokenstyles = {
+--       custom_whitespace = custom_style
+--     }
+--
+-- Notice that the lexer peforms Scintilla/SciTE-style "$()" property expansion.
+-- You may also use "%()". Remember to refrain from assigning specific colors in
+-- styles, but in this case, all user color themes probably define the
+-- "color.grey" property.
+--
+-- ### Line Lexers
+--
+-- By default, lexers match the arbitrary chunks of text passed to them by
+-- Scintilla. These chunks may be a full document, only the visible part of a
+-- document, or even just portions of lines. Some lexers need to match whole
+-- lines. For example, a lexer for the output of a file "diff" needs to know if
+-- the line started with a '+' or '-' and then style the entire line
+-- accordingly. To indicate that your lexer matches by line, use the
+-- `_LEXBYLINE` field:
+--
+--     M._LEXBYLINE = true
+--
+-- Now the input text for the lexer is a single line at a time. Keep in mind
+-- that line lexers do not have the ability to look ahead at subsequent lines.
+--
+-- ### Embedded Lexers
+--
+-- Lexers embed within one another very easily, requiring minimal effort. In the
+-- following sections, the lexer being embedded is called the "child" lexer and
+-- the lexer a child is being embedded in is called the "parent". For example,
+-- consider an HTML lexer and a CSS lexer. Either lexer stands alone for styling
+-- their respective HTML and CSS files. However, CSS can be embedded inside
+-- HTML. In this specific case, the CSS lexer is the "child" lexer with the HTML
+-- lexer being the "parent". Now consider an HTML lexer and a PHP lexer. This
+-- sounds a lot like the case with CSS, but there is a subtle difference: PHP
+-- _embeds itself_ into HTML while CSS is _embedded in_ HTML. This fundamental
+-- difference results in two types of embedded lexers: a parent lexer that
+-- embeds other child lexers in it (like HTML embedding CSS), and a child lexer
+-- that embeds itself within a parent lexer (like PHP embedding itself in HTML).
+--
+-- #### Parent Lexer
+--
+-- Before embedding a child lexer into a parent lexer, the parent lexer needs to
+-- load the child lexer. This is done with the [`lexer.load()`]() function. For
+-- example, loading the CSS lexer within the HTML lexer looks like:
+--
+--     local css = l.load('css')
+--
+-- The next part of the embedding process is telling the parent lexer when to
+-- switch over to the child lexer and when to switch back. The lexer refers to
+-- these indications as the "start rule" and "end rule", respectively, and are
+-- just LPeg patterns. Continuing with the HTML/CSS example, the transition from
+-- HTML to CSS is when the lexer encounters a "style" tag with a "type"
+-- attribute whose value is "text/css":
+--
+--     local css_tag = P('<style') * P(function(input, index)
+--       if input:find('^[^>]+type="text/css"', index) then
+--         return index
+--       end
+--     end)
+--
+-- This pattern looks for the beginning of a "style" tag and searches its
+-- attribute list for the text "`type="text/css"`". (In this simplified example,
+-- the Lua pattern does not consider whitespace between the '=' nor does it
+-- consider that using single quotes is valid.) If there is a match, the
+-- functional pattern returns a value instead of `nil`. In this case, the value
+-- returned does not matter because we ultimately want to style the "style" tag
+-- as an HTML tag, so the actual start rule looks like this:
+--
+--     local css_start_rule = #css_tag * tag
+--
+-- Now that the parent knows when to switch to the child, it needs to know when
+-- to switch back. In the case of HTML/CSS, the switch back occurs when the
+-- lexer encounters an ending "style" tag, though the lexer should still style
+-- the tag as an HTML tag:
+--
+--     local css_end_rule = #P('</style>') * tag
+--
+-- Once the parent loads the child lexer and defines the child's start and end
+-- rules, it embeds the child with the [`lexer.embed_lexer()`]() function:
+--
+--     l.embed_lexer(M, css, css_start_rule, css_end_rule)
+--
+-- The first parameter is the parent lexer object to embed the child in, which
+-- in this case is `M`. The other three parameters are the child lexer object
+-- loaded earlier followed by its start and end rules.
+--
+-- #### Child Lexer
+--
+-- The process for instructing a child lexer to embed itself into a parent is
+-- very similar to embedding a child into a parent: first, load the parent lexer
+-- into the child lexer with the [`lexer.load()`]() function and then create
+-- start and end rules for the child lexer. However, in this case, swap the
+-- lexer object arguments to [`lexer.embed_lexer()`](). For example, in the PHP
+-- lexer:
+--
+--     local html = l.load('html')
+--     local php_start_rule = token('php_tag', '<?php ')
+--     local php_end_rule = token('php_tag', '?>')
+--     l.embed_lexer(html, M, php_start_rule, php_end_rule)
+--
+-- ### Lexers with Complex State
+--
+-- A vast majority of lexers are not stateful and can operate on any chunk of
+-- text in a document. However, there may be rare cases where a lexer does need
+-- to keep track of some sort of persistent state. Rather than using `lpeg.P`
+-- function patterns that set state variables, it is recommended to make use of
+-- Scintilla's built-in, per-line state integers via [`lexer.line_state`](). It
+-- was designed to accommodate up to 32 bit flags for tracking state.
+-- [`lexer.line_from_position()`]() will return the line for any position given
+-- to an `lpeg.P` function pattern. (Any positions derived from that position
+-- argument will also work.)
+--
+-- Writing stateful lexers is beyond the scope of this document.
+--
+-- ## Code Folding
+--
+-- When reading source code, it is occasionally helpful to temporarily hide
+-- blocks of code like functions, classes, comments, etc. This is the concept of
+-- "folding". In the Textadept and SciTE editors for example, little indicators
+-- in the editor margins appear next to code that can be folded at places called
+-- "fold points". When the user clicks an indicator, the editor hides the code
+-- associated with the indicator until the user clicks the indicator again. The
+-- lexer specifies these fold points and what code exactly to fold.
+--
+-- The fold points for most languages occur on keywords or character sequences.
+-- Examples of fold keywords are "if" and "end" in Lua and examples of fold
+-- character sequences are '{', '}', "/\*", and "\*/" in C for code block and
+-- comment delimiters, respectively. However, these fold points cannot occur
+-- just anywhere. For example, lexers should not recognize fold keywords that
+-- appear within strings or comments. The lexer's `_foldsymbols` table allows
+-- you to conveniently define fold points with such granularity. For example,
+-- consider C:
+--
+--     M._foldsymbols = {
+--       [l.OPERATOR] = {['{'] = 1, ['}'] = -1},
+--       [l.COMMENT] = {['/*'] = 1, ['*/'] = -1},
+--       _patterns = {'[{}]', '/%*', '%*/'}
+--     }
+--
+-- The first assignment states that any '{' or '}' that the lexer recognized as
+-- an `lexer.OPERATOR` token is a fold point. The integer `1` indicates the
+-- match is a beginning fold point and `-1` indicates the match is an ending
+-- fold point. Likewise, the second assignment states that any "/\*" or "\*/"
+-- that the lexer recognizes as part of a `lexer.COMMENT` token is a fold point.
+-- The lexer does not consider any occurences of these characters outside their
+-- defined tokens (such as in a string) as fold points. Finally, every
+-- `_foldsymbols` table must have a `_patterns` field that contains a list of
+-- [Lua patterns][] that match fold points. If the lexer encounters text that
+-- matches one of those patterns, the lexer looks up the matched text in its
+-- token's table to determine whether or not the text is a fold point. In the
+-- example above, the first Lua pattern matches any '{' or '}' characters. When
+-- the lexer comes across one of those characters, it checks if the match is an
+-- `lexer.OPERATOR` token. If so, the lexer identifies the match as a fold
+-- point. The same idea applies for the other patterns. (The '%' is in the other
+-- patterns because '\*' is a special character in Lua patterns that needs
+-- escaping.) How do you specify fold keywords? Here is an example for Lua:
+--
+--     M._foldsymbols = {
+--       [l.KEYWORD] = {
+--         ['if'] = 1, ['do'] = 1, ['function'] = 1,
+--         ['end'] = -1, ['repeat'] = 1, ['until'] = -1
+--       },
+--       _patterns = {'%l+'}
+--     }
+--
+-- Any time the lexer encounters a lower case word, if that word is a
+-- `lexer.KEYWORD` token and in the associated list of fold points, the lexer
+-- identifies the word as a fold point.
+--
+-- If your lexer needs to do some additional processing to determine if a match
+-- is a fold point, assign a function that returns an integer. Returning `1` or
+-- `-1` indicates the match is a fold point. Returning `0` indicates it is not.
+-- For example:
+--
+--     local function fold_strange_token(text, pos, line, s, match)
+--       if ... then
+--         return 1 -- beginning fold point
+--       elseif ... then
+--         return -1 -- ending fold point
+--       end
+--       return 0
+--     end
+--
+--     M._foldsymbols = {
+--       ['strange_token'] = {['|'] = fold_strange_token},
+--       _patterns = {'|'}
+--     }
+--
+-- Any time the lexer encounters a '|' that is a "strange_token", it calls the
+-- `fold_strange_token` function to determine if '|' is a fold point. The lexer
+-- calls these functions with the following arguments: the text to identify fold
+-- points in, the beginning position of the current line in the text to fold,
+-- the current line's text, the position in the current line the matched text
+-- starts at, and the matched text itself.
+--
+-- [Lua patterns]: http://www.lua.org/manual/5.2/manual.html#6.4.1
+--
+-- ### Fold by Indentation
+--
+-- Some languages have significant whitespace and/or no delimiters that indicate
+-- fold points. If your lexer falls into this category and you would like to
+-- mark fold points based on changes in indentation, use the
+-- `_FOLDBYINDENTATION` field:
+--
+--     M._FOLDBYINDENTATION = true
+--
+-- ## Using Lexers
+--
+-- ### Textadept
+--
+-- Put your lexer in your *~/.textadept/lexers/* directory so you do not
+-- overwrite it when upgrading Textadept. Also, lexers in this directory
+-- override default lexers. Thus, Textadept loads a user *lua* lexer instead of
+-- the default *lua* lexer. This is convenient for tweaking a default lexer to
+-- your liking. Then add a [file type][] for your lexer if necessary.
+--
+-- [file type]: _M.textadept.file_types.html
+--
+-- ### SciTE
+--
+-- Create a *.properties* file for your lexer and `import` it in either your
+-- *SciTEUser.properties* or *SciTEGlobal.properties*. The contents of the
+-- *.properties* file should contain:
+--
+--     file.patterns.[lexer_name]=[file_patterns]
+--     lexer.$(file.patterns.[lexer_name])=[lexer_name]
+--
+-- where `[lexer_name]` is the name of your lexer (minus the *.lua* extension)
+-- and `[file_patterns]` is a set of file extensions to use your lexer for.
+--
+-- Please note that Lua lexers ignore any styling information in *.properties*
+-- files. Your theme file in the *lexers/themes/* directory contains styling
+-- information.
+--
+-- ## Considerations
+--
+-- ### Performance
+--
+-- There might be some slight overhead when initializing a lexer, but loading a
+-- file from disk into Scintilla is usually more expensive. On modern computer
+-- systems, I see no difference in speed between LPeg lexers and Scintilla's C++
+-- ones. Optimize lexers for speed by re-arranging rules in the `_rules` table
+-- so that the most common rules match first. Do keep in mind that order matters
+-- for similar rules.
+--
+-- ### Limitations
+--
+-- Embedded preprocessor languages like PHP cannot completely embed in their
+-- parent languages in that the parent's tokens do not support start and end
+-- rules. This mostly goes unnoticed, but code like
+--
+--     <div id="<?php echo $id; ?>">
+--
+-- or
+--
+--     <div <?php if ($odd) { echo 'class="odd"'; } ?>>
+--
+-- will not style correctly.
+--
+-- ### Troubleshooting
+--
+-- Errors in lexers can be tricky to debug. Lexers print Lua errors to
+-- `io.stderr` and `_G.print()` statements to `io.stdout`. Running your editor
+-- from a terminal is the easiest way to see errors as they occur.
+--
+-- ### Risks
+--
+-- Poorly written lexers have the ability to crash Scintilla (and thus its
+-- containing application), so unsaved data might be lost. However, I have only
+-- observed these crashes in early lexer development, when syntax errors or
+-- pattern errors are present. Once the lexer actually starts styling text
+-- (either correctly or incorrectly, it does not matter), I have not observed
+-- any crashes.
+--
+-- ### Acknowledgements
+--
+-- Thanks to Peter Odding for his [lexer post][] on the Lua mailing list
+-- that inspired me, and thanks to Roberto Ierusalimschy for LPeg.
+--
+-- [lexer post]: http://lua-users.org/lists/lua-l/2007-04/msg00116.html
+-- @field LEXERPATH (string)
+--   The path used to search for a lexer to load.
+--   Identical in format to Lua's `package.path` string.
+--   The default value is `package.path`.
+-- @field DEFAULT (string)
+--   The token name for default tokens.
+-- @field WHITESPACE (string)
+--   The token name for whitespace tokens.
+-- @field COMMENT (string)
+--   The token name for comment tokens.
+-- @field STRING (string)
+--   The token name for string tokens.
+-- @field NUMBER (string)
+--   The token name for number tokens.
+-- @field KEYWORD (string)
+--   The token name for keyword tokens.
+-- @field IDENTIFIER (string)
+--   The token name for identifier tokens.
+-- @field OPERATOR (string)
+--   The token name for operator tokens.
+-- @field ERROR (string)
+--   The token name for error tokens.
+-- @field PREPROCESSOR (string)
+--   The token name for preprocessor tokens.
+-- @field CONSTANT (string)
+--   The token name for constant tokens.
+-- @field VARIABLE (string)
+--   The token name for variable tokens.
+-- @field FUNCTION (string)
+--   The token name for function tokens.
+-- @field CLASS (string)
+--   The token name for class tokens.
+-- @field TYPE (string)
+--   The token name for type tokens.
+-- @field LABEL (string)
+--   The token name for label tokens.
+-- @field REGEX (string)
+--   The token name for regex tokens.
+-- @field STYLE_CLASS (string)
+--   The style typically used for class definitions.
+-- @field STYLE_COMMENT (string)
+--   The style typically used for code comments.
+-- @field STYLE_CONSTANT (string)
+--   The style typically used for constants.
+-- @field STYLE_ERROR (string)
+--   The style typically used for erroneous syntax.
+-- @field STYLE_FUNCTION (string)
+--   The style typically used for function definitions.
+-- @field STYLE_KEYWORD (string)
+--   The style typically used for language keywords.
+-- @field STYLE_LABEL (string)
+--   The style typically used for labels.
+-- @field STYLE_NUMBER (string)
+--   The style typically used for numbers.
+-- @field STYLE_OPERATOR (string)
+--   The style typically used for operators.
+-- @field STYLE_REGEX (string)
+--   The style typically used for regular expression strings.
+-- @field STYLE_STRING (string)
+--   The style typically used for strings.
+-- @field STYLE_PREPROCESSOR (string)
+--   The style typically used for preprocessor statements.
+-- @field STYLE_TYPE (string)
+--   The style typically used for static types.
+-- @field STYLE_VARIABLE (string)
+--   The style typically used for variables.
+-- @field STYLE_WHITESPACE (string)
+--   The style typically used for whitespace.
+-- @field STYLE_EMBEDDED (string)
+--   The style typically used for embedded code.
+-- @field STYLE_IDENTIFIER (string)
+--   The style typically used for identifier words.
+-- @field STYLE_DEFAULT (string)
+--   The style all styles are based off of.
+-- @field STYLE_LINENUMBER (string)
+--   The style used for all margins except fold margins.
+-- @field STYLE_BRACELIGHT (string)
+--   The style used for highlighted brace characters.
+-- @field STYLE_BRACEBAD (string)
+--   The style used for unmatched brace characters.
+-- @field STYLE_CONTROLCHAR (string)
+--   The style used for control characters.
+--   Color attributes are ignored.
+-- @field STYLE_INDENTGUIDE (string)
+--   The style used for indentation guides.
+-- @field STYLE_CALLTIP (string)
+--   The style used by call tips if [`buffer.call_tip_use_style`]() is set.
+--   Only the font name, size, and color attributes are used.
+-- @field any (pattern)
+--   A pattern that matches any single character.
+-- @field ascii (pattern)
+--   A pattern that matches any ASCII character (codes 0 to 127).
+-- @field extend (pattern)
+--   A pattern that matches any ASCII extended character (codes 0 to 255).
+-- @field alpha (pattern)
+--   A pattern that matches any alphabetic character ('A'-'Z', 'a'-'z').
+-- @field digit (pattern)
+--   A pattern that matches any digit ('0'-'9').
+-- @field alnum (pattern)
+--   A pattern that matches any alphanumeric character ('A'-'Z', 'a'-'z',
+--     '0'-'9').
+-- @field lower (pattern)
+--   A pattern that matches any lower case character ('a'-'z').
+-- @field upper (pattern)
+--   A pattern that matches any upper case character ('A'-'Z').
+-- @field xdigit (pattern)
+--   A pattern that matches any hexadecimal digit ('0'-'9', 'A'-'F', 'a'-'f').
+-- @field cntrl (pattern)
+--   A pattern that matches any control character (ASCII codes 0 to 31).
+-- @field graph (pattern)
+--   A pattern that matches any graphical character ('!' to '~').
+-- @field print (pattern)
+--   A pattern that matches any printable character (' ' to '~').
+-- @field punct (pattern)
+--   A pattern that matches any punctuation character ('!' to '/', ':' to '@',
+--   '[' to ''', '{' to '~').
+-- @field space (pattern)
+--   A pattern that matches any whitespace character ('\t', '\v', '\f', '\n',
+--   '\r', space).
+-- @field newline (pattern)
+--   A pattern that matches any set of end of line characters.
+-- @field nonnewline (pattern)
+--   A pattern that matches any single, non-newline character.
+-- @field nonnewline_esc (pattern)
+--   A pattern that matches any single, non-newline character or any set of end
+--   of line characters escaped with '\'.
+-- @field dec_num (pattern)
+--   A pattern that matches a decimal number.
+-- @field hex_num (pattern)
+--   A pattern that matches a hexadecimal number.
+-- @field oct_num (pattern)
+--   A pattern that matches an octal number.
+-- @field integer (pattern)
+--   A pattern that matches either a decimal, hexadecimal, or octal number.
+-- @field float (pattern)
+--   A pattern that matches a floating point number.
+-- @field word (pattern)
+--   A pattern that matches a typical word. Words begin with a letter or
+--   underscore and consist of alphanumeric and underscore characters.
+-- @field FOLD_BASE (number)
+--   The initial (root) fold level.
+-- @field FOLD_BLANK (number)
+--   Flag indicating that the line is blank.
+-- @field FOLD_HEADER (number)
+--   Flag indicating the line is fold point.
+-- @field fold_level (table, Read-only)
+--   Table of fold level bit-masks for line numbers starting from zero.
+--   Fold level masks are composed of an integer level combined with any of the
+--   following bits:
+--
+--   * `lexer.FOLD_BASE`
+--     The initial fold level.
+--   * `lexer.FOLD_BLANK`
+--     The line is blank.
+--   * `lexer.FOLD_HEADER`
+--     The line is a header, or fold point.
+-- @field indent_amount (table, Read-only)
+--   Table of indentation amounts in character columns, for line numbers
+--   starting from zero.
+-- @field line_state (table)
+--   Table of integer line states for line numbers starting from zero.
+--   Line states can be used by lexers for keeping track of persistent states.
+-- @field property (table)
+--   Map of key-value string pairs.
+-- @field property_expanded (table, Read-only)
+--   Map of key-value string pairs with `$()` and `%()` variable replacement
+--   performed in values.
+-- @field property_int (table, Read-only)
+--   Map of key-value pairs with values interpreted as numbers, or `0` if not
+--   found.
+-- @field style_at (table, Read-only)
+--   Table of style names at positions in the buffer starting from 1.
+module('lexer')]=]
+
+lpeg = require('lpeg')
+local lpeg_P, lpeg_R, lpeg_S, lpeg_V = lpeg.P, lpeg.R, lpeg.S, lpeg.V
+local lpeg_Ct, lpeg_Cc, lpeg_Cp = lpeg.Ct, lpeg.Cc, lpeg.Cp
+local lpeg_Cmt, lpeg_C = lpeg.Cmt, lpeg.C
+local lpeg_match = lpeg.match
+
+M.LEXERPATH = package.path
+
+-- Table of loaded lexers.
+M.lexers = {}
+
+-- Keep track of the last parent lexer loaded. This lexer's rules are used for
+-- proxy lexers (those that load parent and child lexers to embed) that do not
+-- declare a parent lexer.
+local parent_lexer
+
+if not package.searchpath then
+  -- Searches for the given *name* in the given *path*.
+  -- This is an implementation of Lua 5.2's `package.searchpath()` function for
+  -- Lua 5.1.
+  function package.searchpath(name, path)
+    local tried = {}
+    for part in path:gmatch('[^;]+') do
+      local filename = part:gsub('%?', name)
+      local f = io.open(filename, 'r')
+      if f then f:close() return filename end
+      tried[#tried + 1] = ("no file '%s'"):format(filename)
+    end
+    return nil, table.concat(tried, '\n')
+  end
+end
+
+-- Adds a rule to a lexer's current ordered list of rules.
+-- @param lexer The lexer to add the given rule to.
+-- @param name The name associated with this rule. It is used for other lexers
+--   to access this particular rule from the lexer's `_RULES` table. It does not
+--   have to be the same as the name passed to `token`.
+-- @param rule The LPeg pattern of the rule.
+local function add_rule(lexer, id, rule)
+  if not lexer._RULES then
+    lexer._RULES = {}
+    -- Contains an ordered list (by numerical index) of rule names. This is used
+    -- in conjunction with lexer._RULES for building _TOKENRULE.
+    lexer._RULEORDER = {}
+  end
+  lexer._RULES[id] = rule
+  lexer._RULEORDER[#lexer._RULEORDER + 1] = id
+end
+
+-- Adds a new Scintilla style to Scintilla.
+-- @param lexer The lexer to add the given style to.
+-- @param token_name The name of the token associated with this style.
+-- @param style A Scintilla style created from `style()`.
+-- @see style
+local function add_style(lexer, token_name, style)
+  local num_styles = lexer._numstyles
+  if num_styles == 32 then num_styles = num_styles + 8 end -- skip predefined
+  if num_styles >= 255 then print('Too many styles defined (255 MAX)') end
+  lexer._TOKENSTYLES[token_name], lexer._numstyles = num_styles, num_styles + 1
+  lexer._EXTRASTYLES[token_name] = style
+end
+
+-- (Re)constructs `lexer._TOKENRULE`.
+-- @param parent The parent lexer.
+local function join_tokens(lexer)
+  local patterns, order = lexer._RULES, lexer._RULEORDER
+  local token_rule = patterns[order[1]]
+  for i = 2, #order do token_rule = token_rule + patterns[order[i]] end
+  lexer._TOKENRULE = token_rule + M.token(M.DEFAULT, M.any)
+  return lexer._TOKENRULE
+end
+
+-- Adds a given lexer and any of its embedded lexers to a given grammar.
+-- @param grammar The grammar to add the lexer to.
+-- @param lexer The lexer to add.
+local function add_lexer(grammar, lexer, token_rule)
+  local token_rule = join_tokens(lexer)
+  local lexer_name = lexer._NAME
+  for i = 1, #lexer._CHILDREN do
+    local child = lexer._CHILDREN[i]
+    if child._CHILDREN then add_lexer(grammar, child) end
+    local child_name = child._NAME
+    local rules = child._EMBEDDEDRULES[lexer_name]
+    local rules_token_rule = grammar['__'..child_name] or rules.token_rule
+    grammar[child_name] = (-rules.end_rule * rules_token_rule)^0 *
+                          rules.end_rule^-1 * lpeg_V(lexer_name)
+    local embedded_child = '_'..child_name
+    grammar[embedded_child] = rules.start_rule * (-rules.end_rule *
+                              rules_token_rule)^0 * rules.end_rule^-1
+    token_rule = lpeg_V(embedded_child) + token_rule
+  end
+  grammar['__'..lexer_name] = token_rule -- can contain embedded lexer rules
+  grammar[lexer_name] = token_rule^0
+end
+
+-- (Re)constructs `lexer._GRAMMAR`.
+-- @param lexer The parent lexer.
+-- @param initial_rule The name of the rule to start lexing with. The default
+--   value is `lexer._NAME`. Multilang lexers use this to start with a child
+--   rule if necessary.
+local function build_grammar(lexer, initial_rule)
+  local children = lexer._CHILDREN
+  if children then
+    local lexer_name = lexer._NAME
+    if not initial_rule then initial_rule = lexer_name end
+    local grammar = {initial_rule}
+    add_lexer(grammar, lexer)
+    lexer._INITIALRULE = initial_rule
+    lexer._GRAMMAR = lpeg_Ct(lpeg_P(grammar))
+  else
+    lexer._GRAMMAR = lpeg_Ct(join_tokens(lexer)^0)
+  end
+end
+
+local string_upper = string.upper
+-- Default styles.
+local default = {
+  'nothing', 'whitespace', 'comment', 'string', 'number', 'keyword',
+  'identifier', 'operator', 'error', 'preprocessor', 'constant', 'variable',
+  'function', 'class', 'type', 'label', 'regex', 'embedded'
+}
+for i = 1, #default do
+  local name, upper_name = default[i], string_upper(default[i])
+  M[upper_name] = name
+  if not M['STYLE_'..upper_name] then
+    M['STYLE_'..upper_name] = ''
+  end
+end
+-- Predefined styles.
+local predefined = {
+  'default', 'linenumber', 'bracelight', 'bracebad', 'controlchar',
+  'indentguide', 'calltip'
+}
+for i = 1, #predefined do
+  local name, upper_name = predefined[i], string_upper(predefined[i])
+  M[upper_name] = name
+  if not M['STYLE_'..upper_name] then
+    M['STYLE_'..upper_name] = ''
+  end
+end
+
+---
+-- Initializes or loads and returns the lexer of string name *name*.
+-- Scintilla calls this function in order to load a lexer. Parent lexers also
+-- call this function in order to load child lexers and vice-versa. The user
+-- calls this function in order to load a lexer when using Scintillua as a Lua
+-- library.
+-- @param name The name of the lexing language.
+-- @param alt_name The alternate name of the lexing language. This is useful for
+--   embedding the same child lexer with multiple sets of start and end tokens.
+-- @return lexer object
+-- @name load
+function M.load(name, alt_name)
+  if M.lexers[alt_name or name] then return M.lexers[alt_name or name] end
+  parent_lexer = nil -- reset
+
+  -- When using Scintillua as a stand-alone module, the `property` and
+  -- `property_int` tables do not exist (they are not useful). Create them to
+  -- prevent errors from occurring.
+  if not M.property then
+    M.property, M.property_int = {}, setmetatable({}, {
+      __index = function(t, k) return tonumber(M.property[k]) or 0 end,
+      __newindex = function() error('read-only property') end
+    })
+  end
+
+  -- Load the language lexer with its rules, styles, etc.
+  M.WHITESPACE = (alt_name or name)..'_whitespace'
+  local lexer_file, error = package.searchpath('lexers/'..name, M.LEXERPATH)
+  local ok, lexer = pcall(dofile, lexer_file or '')
+  if not ok then
+    return nil
+  end
+  if alt_name then lexer._NAME = alt_name end
+
+  -- Create the initial maps for token names to style numbers and styles.
+  local token_styles = {}
+  for i = 1, #default do token_styles[default[i]] = i - 1 end
+  for i = 1, #predefined do token_styles[predefined[i]] = i + 31 end
+  lexer._TOKENSTYLES, lexer._numstyles = token_styles, #default
+  lexer._EXTRASTYLES = {}
+
+  -- If the lexer is a proxy (loads parent and child lexers to embed) and does
+  -- not declare a parent, try and find one and use its rules.
+  if not lexer._rules and not lexer._lexer then lexer._lexer = parent_lexer end
+
+  -- If the lexer is a proxy or a child that embedded itself, add its rules and
+  -- styles to the parent lexer. Then set the parent to be the main lexer.
+  if lexer._lexer then
+    local l, _r, _s = lexer._lexer, lexer._rules, lexer._tokenstyles
+    if not l._tokenstyles then l._tokenstyles = {} end
+    if _r then
+      for i = 1, #_r do
+        -- Prevent rule id clashes.
+        l._rules[#l._rules + 1] = {lexer._NAME..'_'.._r[i][1], _r[i][2]}
+      end
+    end
+    if _s then
+      for token, style in pairs(_s) do l._tokenstyles[token] = style end
+    end
+    lexer = l
+  end
+
+  -- Add the lexer's styles and build its grammar.
+  if lexer._rules then
+    if lexer._tokenstyles then
+      for token, style in pairs(lexer._tokenstyles) do
+        add_style(lexer, token, style)
+      end
+    end
+    for i = 1, #lexer._rules do
+      add_rule(lexer, lexer._rules[i][1], lexer._rules[i][2])
+    end
+    build_grammar(lexer)
+  end
+  -- Add the lexer's unique whitespace style.
+  add_style(lexer, lexer._NAME..'_whitespace', M.STYLE_WHITESPACE)
+
+  -- Process the lexer's fold symbols.
+  if lexer._foldsymbols and lexer._foldsymbols._patterns then
+    local patterns = lexer._foldsymbols._patterns
+    for i = 1, #patterns do patterns[i] = '()('..patterns[i]..')' end
+  end
+
+  lexer.lex, lexer.fold = M.lex, M.fold
+  M.lexers[alt_name or name] = lexer
+  return lexer
+end
+
+---
+-- Lexes a chunk of text *text* (that has an initial style number of
+-- *init_style*) with lexer *lexer*.
+-- If *lexer* has a `_LEXBYLINE` flag set, the text is lexed one line at a time.
+-- Otherwise the text is lexed as a whole.
+-- @param lexer The lexer object to lex with.
+-- @param text The text in the buffer to lex.
+-- @param init_style The current style. Multiple-language lexers use this to
+--   determine which language to start lexing in.
+-- @return table of token names and positions.
+-- @name lex
+function M.lex(lexer, text, init_style)
+  if not lexer._GRAMMAR then return {M.DEFAULT, #text + 1} end
+  if not lexer._LEXBYLINE then
+    -- For multilang lexers, build a new grammar whose initial_rule is the
+    -- current language.
+    if lexer._CHILDREN then
+      for style, style_num in pairs(lexer._TOKENSTYLES) do
+        if style_num == init_style then
+          local lexer_name = style:match('^(.+)_whitespace') or lexer._NAME
+          if lexer._INITIALRULE ~= lexer_name then
+            build_grammar(lexer, lexer_name)
+          end
+          break
+        end
+      end
+    end
+    return lpeg_match(lexer._GRAMMAR, text)
+  else
+    local tokens = {}
+    local function append(tokens, line_tokens, offset)
+      for i = 1, #line_tokens, 2 do
+        tokens[#tokens + 1] = line_tokens[i]
+        tokens[#tokens + 1] = line_tokens[i + 1] + offset
+      end
+    end
+    local offset = 0
+    local grammar = lexer._GRAMMAR
+    for line in text:gmatch('[^\r\n]*\r?\n?') do
+      local line_tokens = lpeg_match(grammar, line)
+      if line_tokens then append(tokens, line_tokens, offset) end
+      offset = offset + #line
+      -- Use the default style to the end of the line if none was specified.
+      if tokens[#tokens] ~= offset then
+        tokens[#tokens + 1], tokens[#tokens + 2] = 'default', offset + 1
+      end
+    end
+    return tokens
+  end
+end
+
+---
+-- Determines fold points in a chunk of text *text* with lexer *lexer*.
+-- *text* starts at position *start_pos* on line number *start_line* with a
+-- beginning fold level of *start_level* in the buffer. If *lexer* has a `_fold`
+-- function or a `_foldsymbols` table, that field is used to perform folding.
+-- Otherwise, if *lexer* has a `_FOLDBYINDENTATION` field set, or if a
+-- `fold.by.indentation` property is set, folding by indentation is done.
+-- @param lexer The lexer object to fold with.
+-- @param text The text in the buffer to fold.
+-- @param start_pos The position in the buffer *text* starts at, starting at
+--   zero.
+-- @param start_line The line number *text* starts on.
+-- @param start_level The fold level *text* starts on.
+-- @return table of fold levels.
+-- @name fold
+function M.fold(lexer, text, start_pos, start_line, start_level)
+  local folds = {}
+  if text == '' then return folds end
+  local fold = M.property_int['fold'] > 0
+  local FOLD_BASE = M.FOLD_BASE
+  local FOLD_HEADER, FOLD_BLANK  = M.FOLD_HEADER, M.FOLD_BLANK
+  if fold and lexer._fold then
+    return lexer._fold(text, start_pos, start_line, start_level)
+  elseif fold and lexer._foldsymbols then
+    local lines = {}
+    for p, l in (text..'\n'):gmatch('()(.-)\r?\n') do
+      lines[#lines + 1] = {p, l}
+    end
+    local fold_zero_sum_lines = M.property_int['fold.on.zero.sum.lines'] > 0
+    local fold_symbols = lexer._foldsymbols
+    local fold_symbols_patterns = fold_symbols._patterns
+    local style_at, fold_level = M.style_at, M.fold_level
+    local line_num, prev_level = start_line, start_level
+    local current_level = prev_level
+    for i = 1, #lines do
+      local pos, line = lines[i][1], lines[i][2]
+      if line ~= '' then
+        local level_decreased = false
+        for j = 1, #fold_symbols_patterns do
+          for s, match in line:gmatch(fold_symbols_patterns[j]) do
+            local symbols = fold_symbols[style_at[start_pos + pos + s - 1]]
+            local l = symbols and symbols[match]
+            if type(l) == 'function' then l = l(text, pos, line, s, match) end
+            if type(l) == 'number' then
+              current_level = current_level + l
+              if l < 0 and current_level < prev_level then
+                -- Potential zero-sum line. If the level were to go back up on
+                -- the same line, the line may be marked as a fold header.
+                level_decreased = true
+              end
+            end
+          end
+        end
+        folds[line_num] = prev_level
+        if current_level > prev_level then
+          folds[line_num] = prev_level + FOLD_HEADER
+        elseif level_decreased and current_level == prev_level and
+               fold_zero_sum_lines then
+          if line_num > start_line then
+            folds[line_num] = prev_level - 1 + FOLD_HEADER
+          else
+            -- Typing within a zero-sum line.
+            local level = fold_level[line_num - 1] - 1
+            if level > FOLD_HEADER then level = level - FOLD_HEADER end
+            if level > FOLD_BLANK then level = level - FOLD_BLANK end
+            folds[line_num] = level + FOLD_HEADER
+            current_level = current_level + 1
+          end
+        end
+        if current_level < FOLD_BASE then current_level = FOLD_BASE end
+        prev_level = current_level
+      else
+        folds[line_num] = prev_level + FOLD_BLANK
+      end
+      line_num = line_num + 1
+    end
+  elseif fold and (lexer._FOLDBYINDENTATION or
+                   M.property_int['fold.by.indentation'] > 0) then
+    -- Indentation based folding.
+    -- Calculate indentation per line.
+    local indentation = {}
+    for indent, line in (text..'\n'):gmatch('([\t ]*)([^\r\n]*)\r?\n') do
+      indentation[#indentation + 1] = line ~= '' and #indent
+    end
+    -- Find the first non-blank line before start_line. If the current line is
+    -- indented, make that previous line a header and update the levels of any
+    -- blank lines inbetween. If the current line is blank, match the level of
+    -- the previous non-blank line.
+    local current_level = start_level
+    for i = start_line - 1, 0, -1 do
+      local level = M.fold_level[i]
+      if level >= FOLD_HEADER then level = level - FOLD_HEADER end
+      if level < FOLD_BLANK then
+        local indent = M.indent_amount[i]
+        if indentation[1] and indentation[1] > indent then
+          folds[i] = FOLD_BASE + indent + FOLD_HEADER
+          for j = i + 1, start_line - 1 do
+            folds[j] = start_level + FOLD_BLANK
+          end
+        elseif not indentation[1] then
+          current_level = FOLD_BASE + indent
+        end
+        break
+      end
+    end
+    -- Iterate over lines, setting fold numbers and fold flags.
+    for i = 1, #indentation do
+      if indentation[i] then
+        current_level = FOLD_BASE + indentation[i]
+        folds[start_line + i - 1] = current_level
+        for j = i + 1, #indentation do
+          if indentation[j] then
+            if FOLD_BASE + indentation[j] > current_level then
+              folds[start_line + i - 1] = current_level + FOLD_HEADER
+              current_level = FOLD_BASE + indentation[j] -- for any blanks below
+            end
+            break
+          end
+        end
+      else
+        folds[start_line + i - 1] = current_level + FOLD_BLANK
+      end
+    end
+  else
+    -- No folding, reset fold levels if necessary.
+    local current_line = start_line
+    for _ in text:gmatch('\r?\n') do
+      folds[current_line] = start_level
+      current_line = current_line + 1
+    end
+  end
+  return folds
+end
+
+-- The following are utility functions lexers will have access to.
+
+-- Common patterns.
+M.any = lpeg_P(1)
+M.ascii = lpeg_R('\000\127')
+M.extend = lpeg_R('\000\255')
+M.alpha = lpeg_R('AZ', 'az')
+M.digit = lpeg_R('09')
+M.alnum = lpeg_R('AZ', 'az', '09')
+M.lower = lpeg_R('az')
+M.upper = lpeg_R('AZ')
+M.xdigit = lpeg_R('09', 'AF', 'af')
+M.cntrl = lpeg_R('\000\031')
+M.graph = lpeg_R('!~')
+M.print = lpeg_R(' ~')
+M.punct = lpeg_R('!/', ':@', '[\'', '{~')
+M.space = lpeg_S('\t\v\f\n\r ')
+
+M.newline = lpeg_S('\r\n\f')^1
+M.nonnewline = 1 - M.newline
+M.nonnewline_esc = 1 - (M.newline + '\\') + '\\' * M.any
+
+M.dec_num = M.digit^1
+M.hex_num = '0' * lpeg_S('xX') * M.xdigit^1
+M.oct_num = '0' * lpeg_R('07')^1
+M.integer = lpeg_S('+-')^-1 * (M.hex_num + M.oct_num + M.dec_num)
+M.float = lpeg_S('+-')^-1 *
+          ((M.digit^0 * '.' * M.digit^1 + M.digit^1 * '.' * M.digit^0) *
+           (lpeg_S('eE') * lpeg_S('+-')^-1 * M.digit^1)^-1 +
+           (M.digit^1 * lpeg_S('eE') * lpeg_S('+-')^-1 * M.digit^1))
+
+M.word = (M.alpha + '_') * (M.alnum + '_')^0
+
+---
+-- Creates and returns a token pattern with token name *name* and pattern
+-- *patt*.
+-- If *name* is not a predefined token name, its style must be defined in the
+-- lexer's `_tokenstyles` table.
+-- @param name The name of token. If this name is not a predefined token name,
+--   then a style needs to be assiciated with it in the lexer's `_tokenstyles`
+--   table.
+-- @param patt The LPeg pattern associated with the token.
+-- @return pattern
+-- @usage local ws = token(l.WHITESPACE, l.space^1)
+-- @usage local annotation = token('annotation', '@' * l.word)
+-- @name token
+function M.token(name, patt)
+  return lpeg_Cc(name) * patt * lpeg_Cp()
+end
+
+---
+-- Creates and returns a pattern that matches a range of text bounded by
+-- *chars* characters.
+-- This is a convenience function for matching more complicated delimited ranges
+-- like strings with escape characters and balanced parentheses. *single_line*
+-- indicates whether or not the range must be on a single line, *no_escape*
+-- indicates whether or not to ignore '\' as an escape character, and *balanced*
+-- indicates whether or not to handle balanced ranges like parentheses and
+-- requires *chars* to be composed of two characters.
+-- @param chars The character(s) that bound the matched range.
+-- @param single_line Optional flag indicating whether or not the range must be
+--   on a single line.
+-- @param no_escape Optional flag indicating whether or not the range end
+--   character may be escaped by a '\\' character.
+-- @param balanced Optional flag indicating whether or not to match a balanced
+--   range, like the "%b" Lua pattern. This flag only applies if *chars*
+--   consists of two different characters (e.g. "()").
+-- @return pattern
+-- @usage local dq_str_escapes = l.delimited_range('"')
+-- @usage local dq_str_noescapes = l.delimited_range('"', false, true)
+-- @usage local unbalanced_parens = l.delimited_range('()')
+-- @usage local balanced_parens = l.delimited_range('()', false, false, true)
+-- @see nested_pair
+-- @name delimited_range
+function M.delimited_range(chars, single_line, no_escape, balanced)
+  local s = chars:sub(1, 1)
+  local e = #chars == 2 and chars:sub(2, 2) or s
+  local range
+  local b = balanced and s or ''
+  local n = single_line and '\n' or ''
+  if no_escape then
+    local invalid = lpeg_S(e..n..b)
+    range = M.any - invalid
+  else
+    local invalid = lpeg_S(e..n..b) + '\\'
+    range = M.any - invalid + '\\' * M.any
+  end
+  if balanced and s ~= e then
+    return lpeg_P{s * (range + lpeg_V(1))^0 * e}
+  else
+    return s * range^0 * lpeg_P(e)^-1
+  end
+end
+
+---
+-- Creates and returns a pattern that matches pattern *patt* only at the
+-- beginning of a line.
+-- @param patt The LPeg pattern to match on the beginning of a line.
+-- @return pattern
+-- @usage local preproc = token(l.PREPROCESSOR, l.starts_line('#') *
+--   l.nonnewline^0)
+-- @name starts_line
+function M.starts_line(patt)
+  return lpeg_Cmt(lpeg_C(patt), function(input, index, match, ...)
+    local pos = index - #match
+    if pos == 1 then return index, ... end
+    local char = input:sub(pos - 1, pos - 1)
+    if char == '\n' or char == '\r' or char == '\f' then return index, ... end
+  end)
+end
+
+---
+-- Creates and returns a pattern that verifies that string set *s* contains the
+-- first non-whitespace character behind the current match position.
+-- @param s String character set like one passed to `lpeg.S()`.
+-- @return pattern
+-- @usage local regex = l.last_char_includes('+-*!%^&|=,([{') *
+--   l.delimited_range('/')
+-- @name last_char_includes
+function M.last_char_includes(s)
+  s = '['..s:gsub('[-%%%[]', '%%%1')..']'
+  return lpeg_P(function(input, index)
+    if index == 1 then return index end
+    local i = index
+    while input:sub(i - 1, i - 1):match('[ \t\r\n\f]') do i = i - 1 end
+    if input:sub(i - 1, i - 1):match(s) then return index end
+  end)
+end
+
+---
+-- Returns a pattern that matches a balanced range of text that starts with
+-- string *start_chars* and ends with string *end_chars*.
+-- With single-character delimiters, this function is identical to
+-- `delimited_range(start_chars..end_chars, false, true, true)`.
+-- @param start_chars The string starting a nested sequence.
+-- @param end_chars The string ending a nested sequence.
+-- @return pattern
+-- @usage local nested_comment = l.nested_pair('/*', '*/')
+-- @see delimited_range
+-- @name nested_pair
+function M.nested_pair(start_chars, end_chars)
+  local s, e = start_chars, lpeg_P(end_chars)^-1
+  return lpeg_P{s * (M.any - s - end_chars + lpeg_V(1))^0 * e}
+end
+
+---
+-- Creates and returns a pattern that matches any single word in list *words*.
+-- Words consist of alphanumeric and underscore characters, as well as the
+-- characters in string set *word_chars*. *case_insensitive* indicates whether
+-- or not to ignore case when matching words.
+-- This is a convenience function for simplifying a set of ordered choice word
+-- patterns.
+-- @param words A table of words.
+-- @param word_chars Optional string of additional characters considered to be
+--   part of a word. By default, word characters are alphanumerics and
+--   underscores ("%w_" in Lua). This parameter may be `nil` or the empty string
+--   in order to indicate no additional word characters.
+-- @param case_insensitive Optional boolean flag indicating whether or not the
+--   word match is case-insensitive. The default is `false`.
+-- @return pattern
+-- @usage local keyword = token(l.KEYWORD, word_match{'foo', 'bar', 'baz'})
+-- @usage local keyword = token(l.KEYWORD, word_match({'foo-bar', 'foo-baz',
+--   'bar-foo', 'bar-baz', 'baz-foo', 'baz-bar'}, '-', true))
+-- @name word_match
+function M.word_match(words, word_chars, case_insensitive)
+  local word_list = {}
+  for i = 1, #words do
+    word_list[case_insensitive and words[i]:lower() or words[i]] = true
+  end
+  local chars = M.alnum + '_'
+  if word_chars then chars = chars + lpeg_S(word_chars) end
+  return lpeg_Cmt(chars^1, function(input, index, word)
+    if case_insensitive then word = word:lower() end
+    return word_list[word] and index or nil
+  end)
+end
+
+---
+-- Embeds child lexer *child* in parent lexer *parent* using patterns
+-- *start_rule* and *end_rule*, which signal the beginning and end of the
+-- embedded lexer, respectively.
+-- @param parent The parent lexer.
+-- @param child The child lexer.
+-- @param start_rule The pattern that signals the beginning of the embedded
+--   lexer.
+-- @param end_rule The pattern that signals the end of the embedded lexer.
+-- @usage l.embed_lexer(M, css, css_start_rule, css_end_rule)
+-- @usage l.embed_lexer(html, M, php_start_rule, php_end_rule)
+-- @usage l.embed_lexer(html, ruby, ruby_start_rule, ruby_end_rule)
+-- @name embed_lexer
+function M.embed_lexer(parent, child, start_rule, end_rule)
+  -- Add child rules.
+  if not child._EMBEDDEDRULES then child._EMBEDDEDRULES = {} end
+  if not child._RULES then -- creating a child lexer to be embedded
+    if not child._rules then error('Cannot embed language with no rules') end
+    for i = 1, #child._rules do
+      add_rule(child, child._rules[i][1], child._rules[i][2])
+    end
+  end
+  child._EMBEDDEDRULES[parent._NAME] = {
+    ['start_rule'] = start_rule,
+    token_rule = join_tokens(child),
+    ['end_rule'] = end_rule
+  }
+  if not parent._CHILDREN then parent._CHILDREN = {} end
+  local children = parent._CHILDREN
+  children[#children + 1] = child
+  -- Add child styles.
+  if not parent._tokenstyles then parent._tokenstyles = {} end
+  local tokenstyles = parent._tokenstyles
+  tokenstyles[child._NAME..'_whitespace'] = M.STYLE_WHITESPACE
+  if child._tokenstyles then
+    for token, style in pairs(child._tokenstyles) do
+      tokenstyles[token] = style
+    end
+  end
+  child._lexer = parent -- use parent's tokens if child is embedding itself
+  parent_lexer = parent -- use parent's tokens if the calling lexer is a proxy
+end
+
+-- Determines if the previous line is a comment.
+-- This is used for determining if the current comment line is a fold point.
+-- @param prefix The prefix string defining a comment.
+-- @param text The text passed to a fold function.
+-- @param pos The pos passed to a fold function.
+-- @param line The line passed to a fold function.
+-- @param s The s passed to a fold function.
+local function prev_line_is_comment(prefix, text, pos, line, s)
+  local start = line:find('%S')
+  if start < s and not line:find(prefix, start, true) then return false end
+  local p = pos - 1
+  if text:sub(p, p) == '\n' then
+    p = p - 1
+    if text:sub(p, p) == '\r' then p = p - 1 end
+    if text:sub(p, p) ~= '\n' then
+      while p > 1 and text:sub(p - 1, p - 1) ~= '\n' do p = p - 1 end
+      while text:sub(p, p):find('^[\t ]$') do p = p + 1 end
+      return text:sub(p, p + #prefix - 1) == prefix
+    end
+  end
+  return false
+end
+
+-- Determines if the next line is a comment.
+-- This is used for determining if the current comment line is a fold point.
+-- @param prefix The prefix string defining a comment.
+-- @param text The text passed to a fold function.
+-- @param pos The pos passed to a fold function.
+-- @param line The line passed to a fold function.
+-- @param s The s passed to a fold function.
+local function next_line_is_comment(prefix, text, pos, line, s)
+  local p = text:find('\n', pos + s)
+  if p then
+    p = p + 1
+    while text:sub(p, p):find('^[\t ]$') do p = p + 1 end
+    return text:sub(p, p + #prefix - 1) == prefix
+  end
+  return false
+end
+
+---
+-- Returns a fold function (to be used within the lexer's `_foldsymbols` table)
+-- that folds consecutive line comments that start with string *prefix*.
+-- @param prefix The prefix string defining a line comment.
+-- @usage [l.COMMENT] = {['--'] = l.fold_line_comments('--')}
+-- @usage [l.COMMENT] = {['//'] = l.fold_line_comments('//')}
+-- @name fold_line_comments
+function M.fold_line_comments(prefix)
+  local property_int = M.property_int
+  return function(text, pos, line, s)
+    if property_int['fold.line.comments'] == 0 then return 0 end
+    if s > 1 and line:match('^%s*()') < s then return 0 end
+    local prev_line_comment = prev_line_is_comment(prefix, text, pos, line, s)
+    local next_line_comment = next_line_is_comment(prefix, text, pos, line, s)
+    if not prev_line_comment and next_line_comment then return 1 end
+    if prev_line_comment and not next_line_comment then return -1 end
+    return 0
+  end
+end
+
+M.property_expanded = setmetatable({}, {
+  -- Returns the string property value associated with string property *key*,
+  -- replacing any "$()" and "%()" expressions with the values of their keys.
+  __index = function(t, key)
+    return M.property[key]:gsub('[$%%]%b()', function(key)
+      return t[key:sub(3, -2)]
+    end)
+  end,
+  __newindex = function() error('read-only property') end
+})
+
+--[[ The functions and fields below were defined in C.
+
+---
+-- Returns the line number of the line that contains position *pos*, which
+-- starts from 1.
+-- @param pos The position to get the line number of.
+-- @return number
+local function line_from_position(pos) end
+
+---
+-- Individual fields for a lexer instance.
+-- @field _NAME The string name of the lexer.
+-- @field _rules An ordered list of rules for a lexer grammar.
+--   Each rule is a table containing an arbitrary rule name and the LPeg pattern
+--   associated with the rule. The order of rules is important, as rules are
+--   matched sequentially.
+--   Child lexers should not use this table to access and/or modify their
+--   parent's rules and vice-versa. Use the `_RULES` table instead.
+-- @field _tokenstyles A map of non-predefined token names to styles.
+--   Remember to use token names, not rule names. It is recommended to use
+--   predefined styles or color-agnostic styles derived from predefined styles
+--   to ensure compatibility with user color themes.
+-- @field _foldsymbols A table of recognized fold points for the lexer.
+--   Keys are token names with table values defining fold points. Those table
+--   values have string keys of keywords or characters that indicate a fold
+--   point whose values are integers. A value of `1` indicates a beginning fold
+--   point and a value of `-1` indicates an ending fold point. Values can also
+--   be functions that return `1`, `-1`, or `0` (indicating no fold point) for
+--   keys which need additional processing.
+--   There is also a required `_pattern` key whose value is a table containing
+--   Lua pattern strings that match all fold points (the string keys contained
+--   in token name table values). When the lexer encounters text that matches
+--   one of those patterns, the matched text is looked up in its token's table
+--   to determine whether or not it is a fold point.
+-- @field _fold If this function exists in the lexer, it is called for folding
+--   the document instead of using `_foldsymbols` or indentation.
+-- @field _lexer The parent lexer object whose rules should be used. This field
+--   is only necessary to disambiguate a proxy lexer that loaded parent and
+--   child lexers for embedding and ended up having multiple parents loaded.
+-- @field _RULES A map of rule name keys with their associated LPeg pattern
+--   values for the lexer.
+--   This is constructed from the lexer's `_rules` table and accessible to other
+--   lexers for embedded lexer applications like modifying parent or child
+--   rules.
+-- @field _LEXBYLINE Indicates the lexer can only process one whole line of text
+--    (instead of an arbitrary chunk of text) at a time.
+--    The default value is `false`. Line lexers cannot look ahead to subsequent
+--    lines.
+-- @field _FOLDBYINDENTATION Declares the lexer does not define fold points and
+--    that fold points should be calculated based on changes in indentation.
+-- @class table
+-- @name lexer
+local lexer
+]]
+
+return M