Because LC can't do two things at once.

Michael Doub mikedoub at
Sun Feb 22 11:53:17 EST 2015

Thanks for pointing that out Kay.   I was curious to understand the 
differences and I found the following which might be of interest to 
folks.  I cut it from .  As a casual regex 
user I have never had a problem, but your point is still very valid.

-= Mike


JavaScript supports the following modifiers, a subset of those supported 
by Perl:

/g enables "global" matching. When using the replace() method, specify 
this modifier to replace all matches, rather than only the first one.
/i makes the regex match case insensitive.
/m enables "multi-line mode". In this mode, the caret and dollar match 
before and after newlines in the subject string.
You can combine multiple modifiers by stringing them together as in 
/regex/gim. Notably absent is an option to make the dot match line break 

Since forward slashes delimit the regular expression, any forward 
slashes that appear in the regex need to be escaped. E.g. the regex 1/2 
is written as /1\/2/ in JavaScript.

There is indeed no /s modifier to make the dot match all characters, 
including line breaks. To match absolutely any character, you can use 
character class that contains a shorthand class and its negated version, 
such as [\s\S].

JavaScript implements Perl-style regular expressions. However, it lacks 
quite a number of advanced features available in Perl and other modern 
regular expression flavors:

No \A or \Z anchors to match the start or end of the string. Use a caret 
or dollar instead.
Lookbehind is not supported at all. Lookahead is fully supported.
No atomic grouping or possessive quantifiers.
No Unicode support, except for matching single characters with \uFFFF.
No named capturing groups. Use numbered capturing groups instead.
No mode modifiers to set matching options within the regular expression.
No conditionals.
No regular expression comments. Describe your regular expression with 
JavaScript // comments instead, outside the regular expression string.

On 2/22/15 10:18 AM, Kay C Lan wrote:
> On Sun, Feb 22, 2015 at 5:59 AM, Michael Doub <mikedoub at> wrote:
>>  -- great
>> tutorials and lots of examples
>>  -- my favorite testing engine, I love the way it
>> explains what is actually going on
>>  -- a whole library of interesting examples in the
>> community area.
>> It should be noted that only gives you the option to choose
> the flavour of regex to test. Most online regex sites use JavaScript yet LC
> uses the PCRE regex Library so it is possible on other sites that regex
> examples may not give the same results within LC.
> If planning to use regex within LC I strongly recommend using
> and selecting pcre(php) from the top left 3 options.
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