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--- HIGHLIGHT REGULAR EXPRESSIONS MANUAL --------------------------------------
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This file is based on the original Boost API documentation:
http://www.boost.org/doc/libs/1_32_0/libs/regex/doc/syntax.html

Regular expressions can be applied in highlight's syntax definitions.

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Literals
--------

All characters are literals except: ".", "|", "*", "?", "+", "(", ")", "{", "}",
"[", "]", "^", "$" and "\". These characters are literals when preceded by a
"\". A literal is a character that matches itself, or matches the result of
traits_type::translate(), where traits_type is the traits template parameter to
class basic_regex.
Wildcard

The dot character "." matches any single character except : when
match_not_dot_null is passed to the matching algorithms, the dot does not match
a null character; when match_not_dot_newline is passed to the matching
algorithms, then the dot does not match a newline character.


Repeats
-------

A repeat is an expression that is repeated an arbitrary number of times. An
expression followed by "*" can be repeated any number of times including zero.
An expression followed by "+" can be repeated any number of times, but at least
once, if the expression is compiled with the flag regex_constants::bk_plus_qm
then "+" is an ordinary character and "\+" represents a repeat of once or more.
An expression followed by "?" may be repeated zero or one times only, if the
expression is compiled with the flag regex_constants::bk_plus_qm then "?" is an
ordinary character and "\?" represents the repeat zero or once operator. When it
is necessary to specify the minimum and maximum number of repeats explicitly,
the bounds operator "{}" may be used, thus "a{2}" is the letter "a" repeated
exactly twice, "a{2,4}" represents the letter "a" repeated between 2 and 4
times, and "a{2,}" represents the letter "a" repeated at least twice with no
upper limit. Note that there must be no white-space inside the {}, and there is
no upper limit on the values of the lower and upper bounds. When the expression
is compiled with the flag regex_constants::bk_braces then "{" and "}" are
ordinary characters and "\{" and "\}" are used to delimit bounds instead. All
repeat expressions refer to the shortest possible previous sub-expression: a
single character; a character set, or a sub-expression grouped with "()" for
example.

Examples:

"ba*" will match all of "b", "ba", "baaa" etc.

"ba+" will match "ba" or "baaaa" for example but not "b".

"ba?" will match "b" or "ba".

"ba{2,4}" will match "baa", "baaa" and "baaaa".
Non-greedy repeats

Whenever the "extended" regular expression syntax is in use (the default) then
non-greedy repeats are possible by appending a '?' after the repeat; a
non-greedy repeat is one which will match the shortest possible string.

For example to match html tag pairs one could use something like:

"<\s*tagname[^>]*>(.*?)<\s*/tagname\s*>"

In this case $1 will contain the text between the tag pairs, and will be the
shortest possible matching string. 


Parenthesis
-----------

Parentheses serve two purposes, to group items together into a sub-expression,
and to mark what generated the match. For example the expression "(ab)*" would
match all of the string "ababab". The matching algorithms regex_match and
regex_search each take an instance of match_results that reports what caused the
match, on exit from these functions the match_results contains information both
on what the whole expression matched and on what each sub-expression matched. In
the example above match_results[1] would contain a pair of iterators denoting
the final "ab" of the matching string. It is permissible for sub-expressions to
match null strings. If a sub-expression takes no part in a match - for example
if it is part of an alternative that is not taken - then both of the iterators
that are returned for that sub-expression point to the end of the input string,
and the matched parameter for that sub-expression is false. Sub-expressions are
indexed from left to right starting from 1, sub-expression 0 is the whole
expression.


Non-Marking Parenthesis
-----------------------

Sometimes you need to group sub-expressions with parenthesis, but don't want the
parenthesis to spit out another marked sub-expression, in this case a
non-marking parenthesis (?:expression) can be used. For example the following
expression creates no sub-expressions:

"(?:abc)*"
Forward Lookahead Asserts 

There are two forms of these; one for positive forward lookahead asserts, and
one for negative lookahead asserts:

"(?=abc)" matches zero characters only if they are followed by the expression
"abc".

"(?!abc)" matches zero characters only if they are not followed by the
expression "abc".
Independent sub-expressions

"(?>expression)" matches "expression" as an independent atom (the algorithm will
not backtrack into it if a failure occurs later in the expression).


Alternatives
------------

Alternatives occur when the expression can match either one sub-expression or
another, each alternative is separated by a "|", or a "\|" if the flag
regex_constants::bk_vbar is set, or by a newline character if the flag
regex_constants::newline_alt is set. Each alternative is the largest possible
previous sub-expression; this is the opposite behavior from repetition
operators.

Examples:

"a(b|c)" could match "ab" or "ac".

"abc|def" could match "abc" or "def".


Sets
----

A set is a set of characters that can match any single character that is a
member of the set. Sets are delimited by "[" and "]" and can contain literals,
character ranges, character classes, collating elements and equivalence classes.
Set declarations that start with "^" contain the complement of the elements that
follow.

Examples:

Character literals:

"[abc]" will match either of "a", "b", or "c".

"[^abc] will match any character other than "a", "b", or "c".

Character ranges:

"[a-z]" will match any character in the range "a" to "z".

"[^A-Z]" will match any character other than those in the range "A" to "Z".

Note that character ranges are highly locale dependent if the flag
regex_constants::collate is set: they match any character that collates between
the endpoints of the range, ranges will only behave according to ASCII rules
when the default "C" locale is in effect. For example if the library is compiled
with the Win32 localization model, then [a-z] will match the ASCII characters
a-z, and also 'A', 'B' etc, but not 'Z' which collates just after 'z'. This
locale specific behavior is disabled by default (in perl mode), and forces
ranges to collate according to ASCII character code.

Character classes are denoted using the syntax "[:classname:]" within a set
declaration, for example "[[:space:]]" is the set of all whitespace characters.
Character classes are only available if the flag regex_constants::char_classes
is set. The available character classes are:
 

alnum 	Any alpha numeric character. 	 
alpha 	Any alphabetical character a-z and A-Z. Other characters may
	also be included depending upon the locale. 	 
blank 	Any blank character, either a space or a tab. 	 
cntrl 	Any control character. 	 
digit 	Any digit 0-9. 	 
graph 	Any graphical character. 	 
lower 	Any lower case character a-z. Other characters may also be
	included depending upon the locale. 	 
print 	Any printable character. 	 
punct 	Any punctuation character. 	 
space 	Any whitespace character. 	 
upper 	Any upper case character A-Z. Other characters may also be
	included depending upon the locale. 	 
xdigit 	Any hexadecimal digit character, 0-9, a-f and A-F. 	 
word 	Any word character - all alphanumeric characters plus the
	underscore. 	 
Unicode Any character whose code is greater than 255, this
	applies to the wide character traits classes only. 	 

There are some shortcuts that can be used in place of the character classes,
provided the flag regex_constants::escape_in_lists is set then you can use:

\w in place of [:word:]
\s in place of [:space:]
\d in place of [:digit:]
\l in place of [:lower:]
\u in place of [:upper:] 

Collating elements take the general form [.tagname.] inside a set declaration,
where tagname is either a single character, or a name of a collating element,
for example [[.a.]] is equivalent to [a], and [[.comma.]] is equivalent to [,].
The library supports all the standard POSIX collating element names, and in
addition the following digraphs: "ae", "ch", "ll", "ss", "nj", "dz", "lj", each
in lower, upper and title case variations. Multi-character collating elements
can result in the set matching more than one character, for example [[.ae.]]
would match two characters, but note that [^[.ae.]] would only match one
character. 

Equivalence classes take the generalform[=tagname=] inside a set declaration,
where tagname is either a single character, or a name of a collating element,
and matches any character that is a member of the same primary equivalence class
as the collating element [.tagname.]. An equivalence class is a set of
characters that collate the same, a primary equivalence class is a set of
characters whose primary sort key are all the same (for example strings are
typically collated by character, then by accent, and then by case; the primary
sort key then relates to the character, the secondary to the accentation, and
the tertiary to the case). If there is no equivalence class corresponding to
tagname ,then[=tagname=] is exactly the same as [.tagname.]. Unfortunately there
is no locale independent method of obtaining the primary sort key for a
character, except under Win32. For other operating systems the library will
"guess" the primary sort key from the full sort key (obtained from strxfrm), so
equivalence classes are probably best considered broken under any operating
system other than Win32. 

To include a literal "-" in a set declaration then: make it the first character
after the opening "[" or "[^", the endpoint of a range, a collating element, or
if the flag regex_constants::escape_in_lists is set then precede with an escape
character as in "[\-]". To include a literal "[" or "]" or "^" in a set then
make them the endpoint of a range, a collating element, or precede with an
escape character if the flag regex_constants::escape_in_lists is set.


Line anchors
------------

An anchor is something that matches the null string at the start or end of a
line: "^" matches the null string at the start of a line, "$" matches the null
string at the end of a line.


Back references
---------------

A back reference is a reference to a previous sub-expression that has already
been matched, the reference is to what the sub-expression matched, not to the
expression itself. A back reference consists of the escape character "\"
followed by a digit "1" to "9", "\1" refers to the first sub-expression, "\2" to
the second etc. For example the expression "(.*)\1" matches any string that is
repeated about its mid-point for example "abcabc" or "xyzxyz". A back reference
to a sub-expression that did not participate in any match, matches the null
string: NB this is different to some other regular expression matchers. Back
references are only available if the expression is compiled with the flag
regex_constants::bk_refs set.


Word operators
--------------

The following operators are provided for compatibility with the GNU regular
expression library.

"\w" matches any single character that is a member of the "word" character
class, this is identical to the expression "[[:word:]]".

"\W" matches any single character that is not a member of the "word" character
class, this is identical to the expression "[^[:word:]]".

"\<" matches the null string at the start of a word.

"\>" matches the null string at the end of the word.

"\b" matches the null string at either the start or the end of a word.

"\B" matches a null string within a word.

The start of the sequence passed to the matching algorithms is considered to be
a potential start of a word unless the flag match_not_bow is set. The end of the
sequence passed to the matching algorithms is considered to be a potential end
of a word unless the flag match_not_eow is set.


Buffer operators
----------------

The following operators are provided for compatibility with the GNU regular
expression library, and Perl regular expressions:

"\`" matches the start of a buffer.

"\A" matches the start of the buffer.

"\'" matches the end of a buffer.

"\z" matches the end of a buffer.

"\Z" matches the end of a buffer, or possibly one or more new line characters
followed by the end of the buffer.

A buffer is considered to consist of the whole sequence passed to the matching
algorithms, unless the flags match_not_bob or match_not_eob are set.


Escape operator
---------------

The escape character "\" has several meanings.

Inside a set declaration the escape character is a normal character unless the
flag regex_constants::escape_in_lists is set in which case whatever follows the
escape is a literal character regardless of its normal meaning.

The escape operator may introduce an operator for example: back references, or a
word operator.

The escape operator may make the following character normal, for example "\*"
represents a literal "*" rather than the repeat operator.
Single character escape sequences

The following escape sequences are aliases for single characters:
 
Escape sequence 	Character code 	Meaning 	 
\a 	0x07 	Bell character. 	 
\f 	0x0C 	Form feed. 	 
\n 	0x0A 	Newline character. 	 
\r 	0x0D 	Carriage return. 	 
\t 	0x09 	Tab character. 	 
\v 	0x0B 	Vertical tab. 	 
\e 	0x1B 	ASCII Escape character. 	 
\0dd 	0dd 	An octal character code, where dd is one or more octal
		digits. 	 
\xXX 	0xXX 	A hexadecimal character code, where XX is one or more
		hexadecimal digits. 	 
\x{XX} 	0xXX 	A hexadecimal character code, where XX is one or more
		hexadecimal digits, optionally a Unicode character. 	 
\cZ 	z-@ 	An ASCII escape sequence control-Z, where Z is any ASCII
		character greater than or equal to the character code for '@'.


Miscellaneous escape sequences:
-------------------------------

The following are provided mostly for perl compatibility, but note that there
are some differences in the meanings of \l \L \u and \U:
 

\w 	Equivalent to [[:word:]]. 	 
\W 	Equivalent to [^[:word:]]. 	 
\s 	Equivalent to [[:space:]]. 	 
\S 	Equivalent to [^[:space:]]. 	 
\d 	Equivalent to [[:digit:]]. 	 
\D 	Equivalent to [^[:digit:]]. 	 
\l 	Equivalent to [[:lower:]]. 	 
\L 	Equivalent to [^[:lower:]]. 	 
\u 	Equivalent to [[:upper:]]. 	 
\U 	Equivalent to [^[:upper:]]. 	 
\C 	Any single character, equivalent to '.'. 	 
\X 	Match any Unicode combining character sequence, for example "a\x
	0301" (a letter a with an acute). 	 
\Q 	The begin quote operator, everything that follows is treated as
	a literal character until a \E end quote operator is found. 	 
\E 	The end quote operator, terminates a sequence begun with \Q. 

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Examples:
---------

Regex=[[ [A-Z]\w+ ]]
Highlight identifiers beginning with a capital letter.

Regex=[[ [$@%]\w+ ]]
Highlight variables beginning with $, @ or %.

Regex=[[ \$\{(\w+)\}) ]]
or
Regex=[[ \$\{(\w+)\} ]], Group=1
Highlight variable names like ${name}. Only the name is highlighted as keyword.
A sub-expression is used to achieve this effect. If no sub-expression number
is defined (like in the first example above), the right-most sub match
(highest sub id) is returned.

Regex=[[ (\w+)\s*\( ]]
Highlight method names. Note that a sub expression is used again.

Regex=[[STO\xe2\x88\x91]]
Unicode characters in a keyword.

---
Andre Simon
andre.simon1@gmx.de
http://www.andre-simon.de/
http://wiki.andre-simon.de/
