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Added docs for forward lookahead asserts.

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[SVN r12757]
This commit is contained in:
John Maddock
2002-02-08 12:43:59 +00:00
parent f79497c625
commit a5d1526fbb
1 changed files with 12 additions and 3 deletions
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15
syntax.htm
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@ -157,9 +157,18 @@ but don't want the parenthesis to spit out another marked sub-expression,
in this case a non-marking parenthesis (?:expression) can be used. in this case a non-marking parenthesis (?:expression) can be used.
For example the following expression creates no sub-expressions: </p> For example the following expression creates no sub-expressions: </p>
<p>&quot;(?:abc)*&quot; <br> <p>&quot;(?:abc)*&quot;</p>
&nbsp; <br>
&nbsp; </p> <p><em>Forward Lookahead Asserts</em>&nbsp; </p>
<p>There are two forms of these; one for positive forward
lookahead asserts, and one for negative lookahead asserts:</p>
<p>&quot;(?=abc)&quot; matches zero characters only if they are
followed by the expression &quot;abc&quot;.</p>
<p>&quot;(?!abc)&quot; matches zero characters only if they are
not followed by the expression &quot;abc&quot;.</p>
<p><i>Alternatives</i> </p> <p><i>Alternatives</i> </p>