Regular expressions - Revision history

Jsimlo at 20:38, 31 May 2026

2026-05-31T20:38:59Z

Jsimlo at 20:33, 31 May 2026

2026-05-31T20:33:53Z

Jsimlo at 21:37, 29 May 2026

2026-05-29T21:37:32Z

Jsimlo at 21:37, 29 May 2026

2026-05-29T21:37:03Z

Jsimlo at 21:31, 29 May 2026

2026-05-29T21:31:55Z

Jsimlo at 21:31, 29 May 2026

2026-05-29T21:31:23Z

Jsimlo at 21:29, 29 May 2026

2026-05-29T21:29:39Z

Jsimlo at 21:28, 29 May 2026

2026-05-29T21:28:18Z

Jsimlo at 21:25, 29 May 2026

2026-05-29T21:25:44Z

Jsimlo at 21:24, 29 May 2026

2026-05-29T21:24:35Z

@@ Line 375: / Line 375: @@
 :: Look-behind assertions are evaluated by effectively iterating over possible positions "behind" the current matching position, and then matching forward to arrive at the current matching position. While several optimisations and predictive heuristics can be applied to narrow down the possible space being evaluated, the iterative nature cannot be completely avoided, especially with infinite quantifiers. Therefore, a hard limit on the variable size of the "behind" space has to be specified. The default limit is 128 characters, but this can be changed in the {{feature|Config}} by setting {{string|FMaxLBA}} in the {{string|Setts}} section.
 {{example_start}}'''Example:''' INI file overridding the limit for the variable part of look-behind assertions:
 {{example_body}}<nowiki>[Setts]
-FMaxLBA=256
+FMaxLBA=256</nowiki>
 {{example_end}}
+</dd></dl></dd></dl>
 =====Possesive give-nothing-back groups=====

@@ Line 373: / Line 373: @@
 ::* Example: Pattern {{regexp|<nowiki>(?<!fee|foo)bar</nowiki>}} verifies that {{string|bar}} is not preceded by either {{string|fee}} or {{string|foo}}.
-{{todo|Config to change the limit for look-behind assertions.}}
+:: Look-behind assertions are evaluated by effectively iterating over possible positions "behind" the current matching position, and then matching forward to arrive at the current matching position. While several optimisations and predictive heuristics can be applied to narrow down the possible space being evaluated, the iterative nature cannot be completely avoided, especially with infinite quantifiers. Therefore, a hard limit on the variable size of the "behind" space has to be specified. The default limit is 128 characters, but this can be changed in the {{feature|Config}} by setting {{string|FMaxLBA}} in the {{string|Setts}} section.
 =====Possesive give-nothing-back groups=====

@@ Line 362: / Line 362: @@
 :: Zero-width negative look-ahead assertion. This cluster group is the negation of the positive look-ahead. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>foo(?!bar)</nowiki>}} matches {{string|foo}} within {{string|foobaz}} or even just {{string|foo}}, but not within {{string|foobar}}. The look-ahead verifies that {{string|foo}} is not followed by {{string|bar}}.
-::* Example: Pattern {{regexp|<nowiki>foo(?!bar|baz)</nowiki>}} verifies that {{string|foo}} is not followed by neither {{string|bar}} nor {{string|baz}}.
+::* Example: Pattern {{regexp|<nowiki>foo(?!bar|baz)</nowiki>}} verifies that {{string|foo}} is not followed by either {{string|bar}} or {{string|baz}}.
 :; {{string|<nowiki>(?&lt;=pattern)</nowiki>}}

@@ Line 362: / Line 362: @@
 :: Zero-width negative look-ahead assertion. This cluster group is the negation of the positive look-ahead. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>foo(?!bar)</nowiki>}} matches {{string|foo}} within {{string|foobaz}} or even just {{string|foo}}, but not within {{string|foobar}}. The look-ahead verifies that {{string|foo}} is not followed by {{string|bar}}.
 :; {{string|<nowiki>(?&lt;=pattern)</nowiki>}}
@@ Line 370: / Line 371: @@
 :: Zero-width negative look-behind assertion. This cluster group is the negation of the positive look-behind. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>(?<!foo)bar</nowiki>}} matches {{string|bar}} within {{string|feebar}} or even just {{string|bar}}, but not within {{string|foobar}}. The look-behind verifies that {{string|bar}} is not preceded by {{string|foo}}.
 {{todo|Config to change the limit for look-behind assertions.}}

@@ Line 7: / Line 7: @@
 ** [[#Capture groups|Capture groups]]
 *** [[#Cluster groups|Cluster groups]]
 ** [[#Alternations|Alternations]]
 ** [[#Look-around assertions|Look-around assertions]]
 ** [[#Look-behind assertion|Look-behind assertion]]
 ** [[#More escape sequences|More escape sequences]]

@@ Line 363: / Line 363: @@
 ::* Example: Pattern {{regexp|<nowiki>foo(?!bar)</nowiki>}} matches {{string|foo}} within {{string|foobaz}} or even just {{string|foo}}, but not within {{string|foobar}}. The look-ahead verifies that {{string|foo}} is not followed by {{string|bar}}.
-:; {{string|<nowiki>(?<=pattern)</nowiki>}}
+:; {{string|<nowiki>(?&lt;=pattern)</nowiki>}}
 :: Zero-width positive look-behind assertion. This cluster group tries to match right before the current matching position, but it does not advance or recede the current matching position even upon a match, and therefore does not include the text matched by this group in the overall match. It can be used to verify the match is preceded by some other pattern without including any of that in the actual match.
 ::* Example: Pattern {{regexp|<nowiki>(?<=foo)bar</nowiki>}} matches {{string|bar}} within {{string|foobar}}, but not within {{string|feebar}} or within just {{string|bar}}. The look-behind verifies that {{string|bar}} is preceded by {{string|foo}} (but keeping the {{string|foo}} outside of the match).
-:; {{string|<nowiki>(?<!pattern)</nowiki>}}
+:; {{string|<nowiki>(?&lt;!pattern)</nowiki>}}
 :: Zero-width negative look-behind assertion. This cluster group is the negation of the positive look-behind. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>(?<!foo)bar</nowiki>}} matches {{string|bar}} within {{string|feebar}} or even just {{string|bar}}, but not within {{string|foobar}}. The look-behind verifies that {{string|bar}} is not preceded by {{string|foo}}.
@@ Line 375: / Line 375: @@
 =====Other groups=====
-:; {{string|(?&gt;pattern)}}
+:; {{string|<nowiki>(?&gt;pattern)</nowiki>}}
 :: Possesive independent give-nothing-back sub-pattern. This cluster group effectively prevents back-tracking upon matching. Note: Back-tracking is allowed inside of the group before the group ends, but once the group matches as a sub-pattern, further back-tracking inside of that group is not performed and the group can only be ''unmatched'' as a whole at that point. This is effectively a ''grab all you can, and then give nothing back'' operator.

@@ Line 355: / Line 355: @@
 =====Look-around assertions=====
-:; {{string|(?=pattern)}}
+:; {{string|<nowiki>(?=pattern)</nowiki>}}
 :: Zero-width positive look-ahead assertion. This cluster group tries to match at the current matching position, but it does not advance the current matching position even upon a match, and therefore does not include the text matched by this group in the overall match. It can be used to verify the match is followed by some other pattern without including any of that in the actual match.
 ::* Example: Pattern {{regexp|<nowiki>foo(?=bar)</nowiki>}} matches {{string|foo}} within {{string|foobar}}, but not within {{string|foobaz}} or within just {{string|foo}}. The look-ahead verifies that {{string|foo}} is followed by {{string|bar}} (but keeping the {{string|bar}} outside of the match).
-:; {{string|(?!pattern)}}
+:; {{string|<nowiki>(?!pattern)</nowiki>}}
 :: Zero-width negative look-ahead assertion. This cluster group is the negation of the positive look-ahead. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>foo(?!bar)</nowiki>}} matches {{string|foo}} within {{string|foobaz}} or even just {{string|foo}}, but not within {{string|foobar}}. The look-ahead verifies that {{string|foo}} is not followed by {{string|bar}}.
-:; {{string|(?<=pattern)}}
+:; {{string|<nowiki>(?<=pattern)</nowiki>}}
 :: Zero-width positive look-behind assertion. This cluster group tries to match right before the current matching position, but it does not advance or recede the current matching position even upon a match, and therefore does not include the text matched by this group in the overall match. It can be used to verify the match is preceded by some other pattern without including any of that in the actual match.
 ::* Example: Pattern {{regexp|<nowiki>(?<=foo)bar</nowiki>}} matches {{string|bar}} within {{string|foobar}}, but not within {{string|feebar}} or within just {{string|bar}}. The look-behind verifies that {{string|bar}} is preceded by {{string|foo}} (but keeping the {{string|foo}} outside of the match).
-:; {{string|(?<!pattern)}}
+:; {{string|<nowiki>(?<!pattern)</nowiki>}}
 :: Zero-width negative look-behind assertion. This cluster group is the negation of the positive look-behind. It succeeds where the other one would fail, and vice versa.
 ::* Example: Pattern {{regexp|<nowiki>(?<!foo)bar</nowiki>}} matches {{string|bar}} within {{string|feebar}} or even just {{string|bar}}, but not within {{string|foobar}}. The look-behind verifies that {{string|bar}} is not preceded by {{string|foo}}.

@@ Line 382: / Line 382: @@
 :; {{string|\K}}
 :: Removes everything that is to the left of the current matching position from the {{string|\&}} replace back-reference. This effectively provides another type of a look-behind assertion, since it can be used to verify, that a match is preceded by some other pattern.
 =====More escape sequences=====