Hans-Jürgen, wrote:
! Already the first
> two characters
> (?render the expression invalid:(1) An unescaped ? is an
> occurrence indicator, making the preceding entity optional(2) An
> unescaped ( is used for grouping, it does not repesent anything
> => there is no entity preceding the ? which the ? could make optional
> => error
Actually (?: .... ) is a non-capturing group, defined in XPath 3.0 and
XQuery 3.0, based on the same syntax in other languages.
This extension, like a number of others, is useful because the
expression syntax defined by XSD doesn't make use of capturing groups
(there's no \1 or $1 or whatever), and so it doesn't need non-capturing
groups, but in XPath and XQuery they are used.
See e.g.
https://www.w3.org/TR/xpath-functions-30/#regex-syntaxLiam
--
Liam R. E. Quin <
liam@w3.org>
The World Wide Web Consortium (W3C)