On 09/16/19 17:10, Tom Lane wrote:
> I was initially troubled
> by the fact that XML Schema regexps are implicitly anchored, ie must
> match the whole string; that's a huge difference from POSIX. However,
> 19075-6 says that jsonpath like_regex works the same as the LIKE_REGEX
> predicate in SQL; and SQL:2011 "9.18 XQuery regular expression matching"
> defines LIKE_REGEX to work exactly like XQuery's fn:matches function,
> except for some weirdness around newline matching; and that spec
> clearly says that fn:matches treats its pattern argument as NOT anchored.
Yeah, it's a layer cake. XML Schema regexps[1] are implicitly anchored and
don't have any metacharacters devoted to anchoring.
XQuery regexps layer onto[2] XML Schema regexps, adding ^ and $ anchors,
rescinding the implicit anchored-ness, adding reluctant quantifiers,
capturing groups, and back-references, and defining flags.
Then ISO SQL adds a third layer changing the newline semantics, affecting
^, $, ., \s, and \S.
Regards,
-Chap
[1] https://www.w3.org/TR/xmlschema-2/#regexs
[2] https://www.w3.org/TR/xpath-functions-31/#regex-syntax
