GNQuery implements some- but not all – of the standard XPath functions, and quite an extensive list of non-standard ‘extension’ function useful in queries.

Note that when functions are applied to object attributes GNQuery does not compute them directly, but converts them to SQL expressions that are then computed by the underlying SQL server. This means that the precise semantics of the functions can be different from what is specified by the XPath standard, for example according to the XPath standard:

 substring(gn4:title, 1.5, 2.6)

should return three characters of the title – from the second to fourth, but if you execute it using a Microsoft SQL Server based system the result is actually the first and second character of the title.