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-syntax Liam -- Liam R. E. Quin <l...@w3.org> The World Wide Web Consortium (W3C)
