Hi Yasir, The error XPST0051 is correct: If an item type is specified along with “instance of”, its expanded QName must be defined as a generalized atomic type (i.e., either an atomic type or a pure union type) [1]. Hope this helps, Christian [1] https://www.w3.org/TR/xquery-31/#id-matching-item On Fri, Jul 10, 2020 at 4:23 PM Yasir B <bajwaya@gmail.com> wrote:

Hello,

I ran the following query using BaseX 9.3.3 command-line client: 'hello' instance of xs:anyAtomicType the result of the query is `true`.

But if I run this query: 'hello' instance of xs:anySimpleType an error "[XPST0051] Unknown type: xs:anySimpleType" is returned

Similarly, for the query: 'hello' instance of xs:anyType an error "[XPST0051] Unknown type: xs:anyType" is returned

Should xs:anySimpleType and xs:anyType be recognized?

Thank you, Yasir