The error for using e.g. ittp:activeArea on is: Unknown attribute in IMSC namespace '{http://www.w3.org/ns/ttml/profile/imsc1#parameter}activeArea' not permitted on '{http://www.w3.org/ns/ttml}tt'.
I noticed there is an open issue #218 on the need to prune 3rd party namespace items before validation, which is a different issue. (FYI, if #218 were fixed first, it would have hidden this issue.)
The error for using e.g. ittp:activeArea on is: Unknown attribute in IMSC namespace '{http://www.w3.org/ns/ttml/profile/imsc1#parameter}activeArea' not permitted on '{http://www.w3.org/ns/ttml}tt'. I noticed there is an open issue #218 on the need to prune 3rd party namespace items before validation, which is a different issue. (FYI, if #218 were fixed first, it would have hidden this issue.)