Are regex character class set operations (subtraction, intersection) worth the parsing complexity?

Steve steves_list at
Tue Jan 1 12:28:00 PST 2008

BTW, since I mentioned .NET 2.0's character class subtraction syntax, I'll 
note that it actually comes from the W3C's XML Schema regex flavor, and is 
also used in the XPath flavor.

BTW2, I don't actually think it would make much sense to arbitrarily remove 
or limit a feature for the sake of arguably reduced parsing complexity. I 
was more just interested in if others had similar concerns.

From: "Steve" <steves_list at>
Sent: Saturday, December 22, 2007 10:40 PM

> [...] it effectively makes it impossible to parse ES4 regex syntax
> using ES4 regexes (which lack PCRE/.NET/Perl's recursion support). And
> considering that java.util.regex is the only (major) regex library to
> include full character class set operations (.NET only does class
> subtraction), I don't think people would miss the feature that greatly.

> [...] I'm interested in what others think about the character class 
> subtraction
> and intersection features. Personally, I think only allowing one level of
> character class nesting might be a reasonable compromise, especially since
> people could emulate more levels of nesting using lookahead anyway.

More information about the Es4-discuss mailing list