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Is there a particular regular expression engine that is used by mod_rewrite on Apache 1.3?

I want to know so I can get a list of supported and non-supported features.

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For 1.3, it looks like POSIX:

Pattern can be (for Apache 1.1.x a System V8 and for Apache 1.2.x a POSIX) regular expression which gets applied to the current URL.

(I guess we were supposed to assume that meant 1.2 and up.)

For current versions, again from the docs:

mod_rewrite uses the Perl Compatible Regular Expression vocabulary. In this document, we do not attempt to provide a detailed reference to regular expressions.

From there, they provide some basics but mostly point you at Perl's regex docs for full information.

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