In the notes to <analytic>, remove one "only" in "only occur only".
Consider making both clauses into sentences:
The analytic element may only occur within a biblStruct, where its use is mandatory for the description of an analytic level bibliographic item. The element may contain titles and statements of responsibility (author, editor, or other), in any order.
Fixed in rev 11050. Thanks for the report!
Re-opening comment posting here to add a pointer (for the record) to a follow-up bug report: http://purl.org/TEI/BUG/3585188 .