The XML Schema provided for STX is not valid according to the Xerces parser:
cos-nonambig: "http://stx.sourceforge.net/2002/ns":text and "http://stx.sourceforge.net/2002/ns":text (or elements from their substitution group) violate "Unique Particle Attribution". During validation against this schema, ambiguity would be created for those two particles.
The specification for this problem: http://www.w3.org/TR/xmlschema-1/#cos-nonambig
The problem is that the group "template-content" should not reference "text" directly like:
as at the end it references the group:
which also references text in a choice.
So removing the direct "text" reference at line 73 should fix the problem.