Adding upstream version 2.14.0+dfsg.upstream/2.14.0+dfsgupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. -*- mode: rst -*-
+
+.. highlight:: python
+
+====================
+Write your own lexer
+====================
+
+If a lexer for your favorite language is missing in the Pygments package, you
+can easily write your own and extend Pygments.
+
+All you need can be found inside the :mod:`pygments.lexer` module.  As you can
+read in the :doc:`API documentation <api>`, a lexer is a class that is
+initialized with some keyword arguments (the lexer options) and that provides a
+:meth:`.get_tokens_unprocessed()` method which is given a string or unicode
+object with the data to lex.
+
+The :meth:`.get_tokens_unprocessed()` method must return an iterator or iterable
+containing tuples in the form ``(index, token, value)``.  Normally you don't
+need to do this since there are base lexers that do most of the work and that
+you can subclass.
+
+RegexLexer
+==========
+
+The lexer base class used by almost all of Pygments' lexers is the
+:class:`RegexLexer`.  This class allows you to define lexing rules in terms of
+*regular expressions* for different *states*.
+
+States are groups of regular expressions that are matched against the input
+string at the *current position*.  If one of these expressions matches, a
+corresponding action is performed (such as yielding a token with a specific
+type, or changing state), the current position is set to where the last match
+ended and the matching process continues with the first regex of the current
+state.
+
+Lexer states are kept on a stack: each time a new state is entered, the new
+state is pushed onto the stack.  The most basic lexers (like the `DiffLexer`)
+just need one state.
+
+Each state is defined as a list of tuples in the form (`regex`, `action`,
+`new_state`) where the last item is optional.  In the most basic form, `action`
+is a token type (like `Name.Builtin`).  That means: When `regex` matches, emit a
+token with the match text and type `tokentype` and push `new_state` on the state
+stack.  If the new state is ``'#pop'``, the topmost state is popped from the
+stack instead.  To pop more than one state, use ``'#pop:2'`` and so on.
+``'#push'`` is a synonym for pushing a second time the current state on top of
+the stack.
+
+The following example shows the `DiffLexer` from the builtin lexers.  Note that
+it contains some additional attributes `name`, `aliases` and `filenames` which
+aren't required for a lexer.  They are used by the builtin lexer lookup
+functions. ::
+
+    from pygments.lexer import RegexLexer
+    from pygments.token import *
+
+    class DiffLexer(RegexLexer):
+        name = 'Diff'
+        aliases = ['diff']
+        filenames = ['*.diff']
+
+        tokens = {
+            'root': [
+                (r' .*\n', Text),
+                (r'\+.*\n', Generic.Inserted),
+                (r'-.*\n', Generic.Deleted),
+                (r'@.*\n', Generic.Subheading),
+                (r'Index.*\n', Generic.Heading),
+                (r'=.*\n', Generic.Heading),
+                (r'.*\n', Text),
+            ]
+        }
+
+As you can see this lexer only uses one state.  When the lexer starts scanning
+the text, it first checks if the current character is a space.  If this is true
+it scans everything until newline and returns the data as a `Text` token (which
+is the "no special highlighting" token).
+
+If this rule doesn't match, it checks if the current char is a plus sign.  And
+so on.
+
+If no rule matches at the current position, the current char is emitted as an
+`Error` token that indicates a lexing error, and the position is increased by
+one.
+
+
+Adding and testing a new lexer
+==============================
+
+The easiest way to use a new lexer is to use Pygments' support for loading
+the lexer from a file relative to your current directory.
+
+First, change the name of your lexer class to CustomLexer:
+
+.. code-block:: python
+
+    from pygments.lexer import RegexLexer
+    from pygments.token import *
+
+    class CustomLexer(RegexLexer):
+        """All your lexer code goes here!"""
+
+Then you can load and test the lexer from the command line with the additional
+flag ``-x``:
+
+.. code-block:: console
+
+    $ python -m pygments -x -l your_lexer_file.py <inputfile>
+
+To specify a class name other than CustomLexer, append it with a colon:
+
+.. code-block:: console
+
+    $ python -m pygments -x -l your_lexer.py:SomeLexer <inputfile>
+
+Or, using the Python API:
+
+.. code-block:: python
+
+    # For a lexer named CustomLexer
+    your_lexer = load_lexer_from_file(filename, **options)
+
+    # For a lexer named MyNewLexer
+    your_named_lexer = load_lexer_from_file(filename, "MyNewLexer", **options)
+
+When loading custom lexers and formatters, be extremely careful to use only
+trusted files; Pygments will perform the equivalent of ``eval`` on them.
+
+If you only want to use your lexer with the Pygments API, you can import and
+instantiate the lexer yourself, then pass it to :func:`pygments.highlight`.
+
+Use the ``-f`` flag to select a different output format than terminal
+escape sequences. The :class:`pygments.formatters.html.HtmlFormatter` helps
+you with debugging your lexer. You can use the ``debug_token_types`` option
+to display the token types assigned to each part of your input file:
+
+.. code-block:: console
+
+    $ python -m pygments -x -f html -Ofull,debug_token_types -l your_lexer.py:SomeLexer <inputfile>
+
+Hover over each token to see the token type displayed as a tooltip.
+
+To prepare your new lexer for inclusion in the Pygments distribution, so that it
+will be found when passing filenames or lexer aliases from the command line, you
+have to perform the following steps.
+
+First, change to the current directory containing the Pygments source code.  You
+will need to have either an unpacked source tarball, or (preferably) a copy
+cloned from GitHub.
+
+.. code-block:: console
+
+    $ cd pygments
+
+Select a matching module under ``pygments/lexers``, or create a new module for
+your lexer class.
+
+.. note::
+
+  We encourage you to put your lexer class into its own module, unless it's a
+  very small derivative of an already existing lexer.
+
+Next, make sure the lexer is known from outside of the module.  All modules in
+the ``pygments.lexers`` package specify ``__all__``. For example,
+``esoteric.py`` sets::
+
+    __all__ = ['BrainfuckLexer', 'BefungeLexer', ...]
+
+Add the name of your lexer class to this list (or create the list if your lexer
+is the only class in the module).
+
+Finally the lexer can be made publicly known by rebuilding the lexer mapping.
+In the root directory of the source (where the ``Makefile`` is located), run:
+
+.. code-block:: console
+
+    $ make mapfiles
+
+To test the new lexer, store an example file in
+``tests/examplefiles/<alias>``.  For example, to test your
+``DiffLexer``, add a ``tests/examplefiles/diff/example.diff`` containing a
+sample diff output.  To (re)generate the lexer output which the file is checked
+against, use the command ``pytest tests/examplefiles/diff --update-goldens``.
+
+Now you can use ``python -m pygments`` from the current root of the checkout to
+render your example to HTML:
+
+.. code-block:: console
+
+    $ python -m pygments -O full -f html -o /tmp/example.html tests/examplefiles/diff/example.diff
+
+Note that this explicitly calls the ``pygments`` module in the current
+directory. This ensures your modifications are used. Otherwise a possibly
+already installed, unmodified version without your new lexer would have been
+called from the system search path (``$PATH``).
+
+To view the result, open ``/tmp/example.html`` in your browser.
+
+Once the example renders as expected, you should run the complete test suite:
+
+.. code-block:: console
+
+    $ make test
+
+It also tests that your lexer fulfills the lexer API and certain invariants,
+such as that the concatenation of all token text is the same as the input text.
+
+
+Regex Flags
+===========
+
+You can either define regex flags locally in the regex (``r'(?x)foo bar'``) or
+globally by adding a `flags` attribute to your lexer class.  If no attribute is
+defined, it defaults to `re.MULTILINE`.  For more information about regular
+expression flags see the page about `regular expressions`_ in the Python
+documentation.
+
+.. _regular expressions: https://docs.python.org/library/re.html#regular-expression-syntax
+
+
+Scanning multiple tokens at once
+================================
+
+So far, the `action` element in the rule tuple of regex, action and state has
+been a single token type.  Now we look at the first of several other possible
+values.
+
+Here is a more complex lexer that highlights INI files.  INI files consist of
+sections, comments and ``key = value`` pairs::
+
+    from pygments.lexer import RegexLexer, bygroups
+    from pygments.token import *
+
+    class IniLexer(RegexLexer):
+        name = 'INI'
+        aliases = ['ini', 'cfg']
+        filenames = ['*.ini', '*.cfg']
+
+        tokens = {
+            'root': [
+                (r'\s+', Text),
+                (r';.*?$', Comment),
+                (r'\[.*?\]$', Keyword),
+                (r'(.*?)(\s*)(=)(\s*)(.*?)$',
+                 bygroups(Name.Attribute, Text, Operator, Text, String))
+            ]
+        }
+
+The lexer first looks for whitespace, comments and section names.  Later it
+looks for a line that looks like a key, value pair, separated by an ``'='``
+sign, and optional whitespace.
+
+The `bygroups` helper yields each capturing group in the regex with a different
+token type.  First the `Name.Attribute` token, then a `Text` token for the
+optional whitespace, after that a `Operator` token for the equals sign. Then a
+`Text` token for the whitespace again.  The rest of the line is returned as
+`String`.
+
+Note that for this to work, every part of the match must be inside a capturing
+group (a ``(...)``), and there must not be any nested capturing groups.  If you
+nevertheless need a group, use a non-capturing group defined using this syntax:
+``(?:some|words|here)`` (note the ``?:`` after the beginning parenthesis).
+
+If you find yourself needing a capturing group inside the regex which shouldn't
+be part of the output but is used in the regular expressions for backreferencing
+(eg: ``r'(<(foo|bar)>)(.*?)(</\2>)'``), you can pass `None` to the bygroups
+function and that group will be skipped in the output.
+
+
+Changing states
+===============
+
+Many lexers need multiple states to work as expected.  For example, some
+languages allow multiline comments to be nested.  Since this is a recursive
+pattern it's impossible to lex just using regular expressions.
+
+Here is a lexer that recognizes C++ style comments (multi-line with ``/* */``
+and single-line with ``//`` until end of line)::
+
+    from pygments.lexer import RegexLexer
+    from pygments.token import *
+
+    class CppCommentLexer(RegexLexer):
+        name = 'Example Lexer with states'
+
+        tokens = {
+            'root': [
+                (r'[^/]+', Text),
+                (r'/\*', Comment.Multiline, 'comment'),
+                (r'//.*?$', Comment.Singleline),
+                (r'/', Text)
+            ],
+            'comment': [
+                (r'[^*/]+', Comment.Multiline),
+                (r'/\*', Comment.Multiline, '#push'),
+                (r'\*/', Comment.Multiline, '#pop'),
+                (r'[*/]', Comment.Multiline)
+            ]
+        }
+
+This lexer starts lexing in the ``'root'`` state. It tries to match as much as
+possible until it finds a slash (``'/'``).  If the next character after the slash
+is an asterisk (``'*'``) the `RegexLexer` sends those two characters to the
+output stream marked as `Comment.Multiline` and continues lexing with the rules
+defined in the ``'comment'`` state.
+
+If there wasn't an asterisk after the slash, the `RegexLexer` checks if it's a
+Singleline comment (i.e. followed by a second slash).  If this also wasn't the
+case it must be a single slash, which is not a comment starter (the separate
+regex for a single slash must also be given, else the slash would be marked as
+an error token).
+
+Inside the ``'comment'`` state, we do the same thing again.  Scan until the
+lexer finds a star or slash.  If it's the opening of a multiline comment, push
+the ``'comment'`` state on the stack and continue scanning, again in the
+``'comment'`` state.  Else, check if it's the end of the multiline comment.  If
+yes, pop one state from the stack.
+
+Note: If you pop from an empty stack you'll get an `IndexError`.  (There is an
+easy way to prevent this from happening: don't ``'#pop'`` in the root state).
+
+If the `RegexLexer` encounters a newline that is flagged as an error token, the
+stack is emptied and the lexer continues scanning in the ``'root'`` state.  This
+can help producing error-tolerant highlighting for erroneous input, e.g. when a
+single-line string is not closed.
+
+
+Advanced state tricks
+=====================
+
+There are a few more things you can do with states:
+
+- You can push multiple states onto the stack if you give a tuple instead of a
+  simple string as the third item in a rule tuple.  For example, if you want to
+  match a comment containing a directive, something like:
+
+  .. code-block:: text
+
+      /* <processing directive>    rest of comment */
+
+  you can use this rule::
+
+      tokens = {
+          'root': [
+              (r'/\* <', Comment, ('comment', 'directive')),
+              ...
+          ],
+          'directive': [
+              (r'[^>]+', Comment.Directive),
+              (r'>', Comment, '#pop'),
+          ],
+          'comment': [
+              (r'[^*]+', Comment),
+              (r'\*/', Comment, '#pop'),
+              (r'\*', Comment),
+          ]
+      }
+
+  When this encounters the above sample, first ``'comment'`` and ``'directive'``
+  are pushed onto the stack, then the lexer continues in the directive state
+  until it finds the closing ``>``, then it continues in the comment state until
+  the closing ``*/``.  Then, both states are popped from the stack again and
+  lexing continues in the root state.
+
+  .. versionadded:: 0.9
+     The tuple can contain the special ``'#push'`` and ``'#pop'`` (but not
+     ``'#pop:n'``) directives.
+
+
+- You can include the rules of a state in the definition of another.  This is
+  done by using `include` from `pygments.lexer`::
+
+      from pygments.lexer import RegexLexer, bygroups, include
+      from pygments.token import *
+
+      class ExampleLexer(RegexLexer):
+          tokens = {
+              'comments': [
+                  (r'(?s)/\*.*?\*/', Comment),
+                  (r'//.*?\n', Comment),
+              ],
+              'root': [
+                  include('comments'),
+                  (r'(function)( )(\w+)( )({)',
+                   bygroups(Keyword, Whitespace, Name, Whitespace, Punctuation), 'function'),
+                  (r'.*\n', Text),
+              ],
+              'function': [
+                  (r'[^}/]+', Text),
+                  include('comments'),
+                  (r'/', Text),
+                  (r'\}', Punctuation, '#pop'),
+              ]
+          }
+
+  This is a hypothetical lexer for a language that consist of functions and
+  comments.  Because comments can occur at toplevel and in functions, we need
+  rules for comments in both states.  As you can see, the `include` helper saves
+  repeating rules that occur more than once (in this example, the state
+  ``'comment'`` will never be entered by the lexer, as it's only there to be
+  included in ``'root'`` and ``'function'``).
+
+- Sometimes, you may want to "combine" a state from existing ones.  This is
+  possible with the `combined` helper from `pygments.lexer`.
+
+  If you, instead of a new state, write ``combined('state1', 'state2')`` as the
+  third item of a rule tuple, a new anonymous state will be formed from state1
+  and state2 and if the rule matches, the lexer will enter this state.
+
+  This is not used very often, but can be helpful in some cases, such as the
+  `PythonLexer`'s string literal processing.
+
+- If you want your lexer to start lexing in a different state you can modify the
+  stack by overriding the `get_tokens_unprocessed()` method::
+
+      from pygments.lexer import RegexLexer
+
+      class ExampleLexer(RegexLexer):
+          tokens = {...}
+
+          def get_tokens_unprocessed(self, text, stack=('root', 'otherstate')):
+              for item in RegexLexer.get_tokens_unprocessed(self, text, stack):
+                  yield item
+
+  Some lexers like the `PhpLexer` use this to make the leading ``<?php``
+  preprocessor comments optional.  Note that you can crash the lexer easily by
+  putting values into the stack that don't exist in the token map.  Also
+  removing ``'root'`` from the stack can result in strange errors!
+
+- In some lexers, a state should be popped if anything is encountered that isn't
+  matched by a rule in the state.  You could use an empty regex at the end of
+  the state list, but Pygments provides a more obvious way of spelling that:
+  ``default('#pop')`` is equivalent to ``('', Text, '#pop')``.
+
+  .. versionadded:: 2.0
+
+
+Subclassing lexers derived from RegexLexer
+==========================================
+
+.. versionadded:: 1.6
+
+Sometimes multiple languages are very similar, but should still be lexed by
+different lexer classes.
+
+When subclassing a lexer derived from RegexLexer, the ``tokens`` dictionaries
+defined in the parent and child class are merged.  For example::
+
+      from pygments.lexer import RegexLexer, inherit
+      from pygments.token import *
+
+      class BaseLexer(RegexLexer):
+          tokens = {
+              'root': [
+                  ('[a-z]+', Name),
+                  (r'/\*', Comment, 'comment'),
+                  ('"', String, 'string'),
+                  (r'\s+', Text),
+              ],
+              'string': [
+                  ('[^"]+', String),
+                  ('"', String, '#pop'),
+              ],
+              'comment': [
+                  ...
+              ],
+          }
+
+      class DerivedLexer(BaseLexer):
+          tokens = {
+              'root': [
+                  ('[0-9]+', Number),
+                  inherit,
+              ],
+              'string': [
+                  (r'[^"\\]+', String),
+                  (r'\\.', String.Escape),
+                  ('"', String, '#pop'),
+              ],
+          }
+
+The `BaseLexer` defines two states, lexing names and strings.  The
+`DerivedLexer` defines its own tokens dictionary, which extends the definitions
+of the base lexer:
+
+* The "root" state has an additional rule and then the special object `inherit`,
+  which tells Pygments to insert the token definitions of the parent class at
+  that point.
+
+* The "string" state is replaced entirely, since there is not `inherit` rule.
+
+* The "comment" state is inherited entirely.
+
+
+Using multiple lexers
+=====================
+
+Using multiple lexers for the same input can be tricky.  One of the easiest
+combination techniques is shown here: You can replace the action entry in a rule
+tuple with a lexer class.  The matched text will then be lexed with that lexer,
+and the resulting tokens will be yielded.
+
+For example, look at this stripped-down HTML lexer::
+
+    from pygments.lexer import RegexLexer, bygroups, using
+    from pygments.token import *
+    from pygments.lexers.javascript import JavascriptLexer
+
+    class HtmlLexer(RegexLexer):
+        name = 'HTML'
+        aliases = ['html']
+        filenames = ['*.html', '*.htm']
+
+        flags = re.IGNORECASE | re.DOTALL
+        tokens = {
+            'root': [
+                ('[^<&]+', Text),
+                ('&.*?;', Name.Entity),
+                (r'<\s*script\s*', Name.Tag, ('script-content', 'tag')),
+                (r'<\s*[a-zA-Z0-9:]+', Name.Tag, 'tag'),
+                (r'<\s*/\s*[a-zA-Z0-9:]+\s*>', Name.Tag),
+            ],
+            'script-content': [
+                (r'(.+?)(<\s*/\s*script\s*>)',
+                 bygroups(using(JavascriptLexer), Name.Tag),
+                 '#pop'),
+            ]
+        }
+
+Here the content of a ``<script>`` tag is passed to a newly created instance of
+a `JavascriptLexer` and not processed by the `HtmlLexer`.  This is done using
+the `using` helper that takes the other lexer class as its parameter.
+
+Note the combination of `bygroups` and `using`.  This makes sure that the
+content up to the ``</script>`` end tag is processed by the `JavascriptLexer`,
+while the end tag is yielded as a normal token with the `Name.Tag` type.
+
+Also note the ``(r'<\s*script\s*', Name.Tag, ('script-content', 'tag'))`` rule.
+Here, two states are pushed onto the state stack, ``'script-content'`` and
+``'tag'``.  That means that first ``'tag'`` is processed, which will lex
+attributes and the closing ``>``, then the ``'tag'`` state is popped and the
+next state on top of the stack will be ``'script-content'``.
+
+Since you cannot refer to the class currently being defined, use `this`
+(imported from `pygments.lexer`) to refer to the current lexer class, i.e.
+``using(this)``.  This construct may seem unnecessary, but this is often the
+most obvious way of lexing arbitrary syntax between fixed delimiters without
+introducing deeply nested states.
+
+The `using()` helper has a special keyword argument, `state`, which works as
+follows: if given, the lexer to use initially is not in the ``"root"`` state,
+but in the state given by this argument.  This does not work with advanced
+`RegexLexer` subclasses such as `ExtendedRegexLexer` (see below).
+
+Any other keywords arguments passed to `using()` are added to the keyword
+arguments used to create the lexer.
+
+
+Delegating Lexer
+================
+
+Another approach for nested lexers is the `DelegatingLexer` which is for example
+used for the template engine lexers.  It takes two lexers as arguments on
+initialisation: a `root_lexer` and a `language_lexer`.
+
+The input is processed as follows: First, the whole text is lexed with the
+`language_lexer`.  All tokens yielded with the special type of ``Other`` are
+then concatenated and given to the `root_lexer`.  The language tokens of the
+`language_lexer` are then inserted into the `root_lexer`'s token stream at the
+appropriate positions. ::
+
+    from pygments.lexer import DelegatingLexer
+    from pygments.lexers.web import HtmlLexer, PhpLexer
+
+    class HtmlPhpLexer(DelegatingLexer):
+        def __init__(self, **options):
+            super().__init__(HtmlLexer, PhpLexer, **options)
+
+This procedure ensures that e.g. HTML with template tags in it is highlighted
+correctly even if the template tags are put into HTML tags or attributes.
+
+If you want to change the needle token ``Other`` to something else, you can give
+the lexer another token type as the third parameter::
+
+    DelegatingLexer.__init__(MyLexer, OtherLexer, Text, **options)
+
+
+Callbacks
+=========
+
+Sometimes the grammar of a language is so complex that a lexer would be unable
+to process it just by using regular expressions and stacks.
+
+For this, the `RegexLexer` allows callbacks to be given in rule tuples, instead
+of token types (`bygroups` and `using` are nothing else but preimplemented
+callbacks).  The callback must be a function taking two arguments:
+
+* the lexer itself
+* the match object for the last matched rule
+
+The callback must then return an iterable of (or simply yield) ``(index,
+tokentype, value)`` tuples, which are then just passed through by
+`get_tokens_unprocessed()`.  The ``index`` here is the position of the token in
+the input string, ``tokentype`` is the normal token type (like `Name.Builtin`),
+and ``value`` the associated part of the input string.
+
+You can see an example here::
+
+    from pygments.lexer import RegexLexer
+    from pygments.token import Generic
+
+    class HypotheticLexer(RegexLexer):
+
+        def headline_callback(lexer, match):
+            equal_signs = match.group(1)
+            text = match.group(2)
+            yield match.start(), Generic.Headline, equal_signs + text + equal_signs
+
+        tokens = {
+            'root': [
+                (r'(=+)(.*?)(\1)', headline_callback)
+            ]
+        }
+
+If the regex for the `headline_callback` matches, the function is called with
+the match object.  Note that after the callback is done, processing continues
+normally, that is, after the end of the previous match.  The callback has no
+possibility to influence the position.
+
+There are not really any simple examples for lexer callbacks, but you can see
+them in action e.g. in the `SMLLexer` class in `ml.py`_.
+
+.. _ml.py: https://github.com/pygments/pygments/blob/master/pygments/lexers/ml.py
+
+
+The ExtendedRegexLexer class
+============================
+
+The `RegexLexer`, even with callbacks, unfortunately isn't powerful enough for
+the funky syntax rules of languages such as Ruby.
+
+But fear not; even then you don't have to abandon the regular expression
+approach: Pygments has a subclass of `RegexLexer`, the `ExtendedRegexLexer`.
+All features known from RegexLexers are available here too, and the tokens are
+specified in exactly the same way, *except* for one detail:
+
+The `get_tokens_unprocessed()` method holds its internal state data not as local
+variables, but in an instance of the `pygments.lexer.LexerContext` class, and
+that instance is passed to callbacks as a third argument. This means that you
+can modify the lexer state in callbacks.
+
+The `LexerContext` class has the following members:
+
+* `text` -- the input text
+* `pos` -- the current starting position that is used for matching regexes
+* `stack` -- a list containing the state stack
+* `end` -- the maximum position to which regexes are matched, this defaults to
+  the length of `text`
+
+Additionally, the `get_tokens_unprocessed()` method can be given a
+`LexerContext` instead of a string and will then process this context instead of
+creating a new one for the string argument.
+
+Note that because you can set the current position to anything in the callback,
+it won't be automatically be set by the caller after the callback is finished.
+For example, this is how the hypothetical lexer above would be written with the
+`ExtendedRegexLexer`::
+
+    from pygments.lexer import ExtendedRegexLexer
+    from pygments.token import Generic
+
+    class ExHypotheticLexer(ExtendedRegexLexer):
+
+        def headline_callback(lexer, match, ctx):
+            equal_signs = match.group(1)
+            text = match.group(2)
+            yield match.start(), Generic.Headline, equal_signs + text + equal_signs
+            ctx.pos = match.end()
+
+        tokens = {
+            'root': [
+                (r'(=+)(.*?)(\1)', headline_callback)
+            ]
+        }
+
+This might sound confusing (and it can really be). But it is needed, and for an
+example look at the Ruby lexer in `ruby.py`_.
+
+.. _ruby.py: https://github.com/pygments/pygments/blob/master/pygments/lexers/ruby.py
+
+
+Handling Lists of Keywords
+==========================
+
+For a relatively short list (hundreds) you can construct an optimized regular
+expression directly using ``words()`` (longer lists, see next section).  This
+function handles a few things for you automatically, including escaping
+metacharacters and Python's first-match rather than longest-match in
+alternations.  Feel free to put the lists themselves in
+``pygments/lexers/_$lang_builtins.py`` (see examples there), and generated by
+code if possible.
+
+An example of using ``words()`` is something like::
+
+    from pygments.lexer import RegexLexer, words, Name
+
+    class MyLexer(RegexLexer):
+
+        tokens = {
+            'root': [
+                (words(('else', 'elseif'), suffix=r'\b'), Name.Builtin),
+                (r'\w+', Name),
+            ],
+        }
+
+As you can see, you can add ``prefix`` and ``suffix`` parts to the constructed
+regex.
+
+
+Modifying Token Streams
+=======================
+
+Some languages ship a lot of builtin functions (for example PHP).  The total
+amount of those functions differs from system to system because not everybody
+has every extension installed.  In the case of PHP there are over 3000 builtin
+functions.  That's an incredibly huge amount of functions, much more than you
+want to put into a regular expression.
+
+But because only `Name` tokens can be function names this is solvable by
+overriding the ``get_tokens_unprocessed()`` method.  The following lexer
+subclasses the `PythonLexer` so that it highlights some additional names as
+pseudo keywords::
+
+    from pygments.lexers.python import PythonLexer
+    from pygments.token import Name, Keyword
+
+    class MyPythonLexer(PythonLexer):
+        EXTRA_KEYWORDS = set(('foo', 'bar', 'foobar', 'barfoo', 'spam', 'eggs'))
+
+        def get_tokens_unprocessed(self, text):
+            for index, token, value in PythonLexer.get_tokens_unprocessed(self, text):
+                if token is Name and value in self.EXTRA_KEYWORDS:
+                    yield index, Keyword.Pseudo, value
+                else:
+                    yield index, token, value
+
+The `PhpLexer` and `LuaLexer` use this method to resolve builtin functions.