From @davemevans's comment:
Seems that schema file available at that link has not been updated to match the current (4th) edition of the DASH spec - it only seems to match the 2nd edition.
4th Edition schema is available at https://standards.iso.org/iso-iec/23009/-1/ed-4/en/DASHSchema-4th-Ed.zip (link is in the spec) and includes endNumber.
Originally posted by @davemevans in #57 (comment)
We need to update our schema file and make it work.
From @davemevans's comment:
We need to update our schema file and make it work.