Re: [xsl] why matches($title,'.*?(\.|,)\s*$')) can perform so much worse than matches($title,'(\.|,)\s*$'))

[Michael Kay <mike@xxxxxxxxxxxx>]

> It would be perfectly valid (and sensible) for a query processor to 
> realise that the two expressions you gave were equivalent and so not 
> perform n^2 tests, but I am unaware of a processor that makes these 
> kinds of optimizations to regular expressions.

Actually I've heard it said that there's a wide variation between 
different regex engines in how well they handle this kind of thing. See 
for example here:

http://swtch.com/~rsc/regexp/regexp1.html

The article at

http://eyalsch.wordpress.com/2009/05/21/regex/

is also useful.

Michael Kay
Saxonica