cross document id idref pair checks

I have  <a href="file.ext#id-val">
in document one.

I need to check that the parent of the element with id 'id-val',
in 'file.ext' has parent <par>, when my input document is document one.

Can id use the id() function across documents somehow?
It doesn't seem unreasonable, but the logic is far from obvious.

Any suggestions appreciated.

TIA DaveP


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