question on representing XML in specs

I've been trying to find out whether the convention used in
some W3C specs for representing XML is a published and
royalty-free convention and whether it has a name. I would
quite like to use it in some XML syntax specifications and
to be able to add a reference to say what convention is being
used but I cannot find what it is called and whether it is
formally defined. An example of the representation is in the
document for XML Schema http://www.w3.org/TR/xmlschema-1/
where there is an "XML Representation Summary" like this:

<example
  count = integer
  size = (large | medium | small) : medium>
  Content: (all | any*)
</example>

Any pointers much appreciated. Is it OK to use it for non-W3C
specifications?

Thanks

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Stephen D Green