Per Sebastian, add the following points to the instructions for adding Schematron constraints in TCW20 ("How to edit the Guidelines"):
* break the message up into shortish lines (for documentation purposes if nothing else)
* use <name/> to give the context of the situation where the test ran (rather than just the word eg "seg") - this is so that in some future implementation <name/> might be treated differently
* refer to attributes using the @name convention, rather than quotes or plain names
In view of recent build problems, it might also be a good idea to suggest that the context node for a constraint should always be an element, not an attribute (see email discussion 2012-01-11ff).