[xsl] How to allow element to appear 0, or 2 or more times (but not once)?

[<mlcook@xxxxxxxxxx>]

I have a working schema for data that we use, and want to expand it to
do more checking on the XML elements.

We have a particular data element, say <FM>, that is not required to
appear in our data, but if it does, it must appear at least twice, and
possibly more.

That is, I want to detect a singular occurrence of <FM> during file
validation.

There are other sibling elements along with <FM>.

Can this be done, and can it be done with the schema itself, or with
uniqueness constraints, or???

I'm using Oxygen 9.1 and XSLT 2.0.

Thanks, Mike


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