In all cases the document defines a region, so there is no default region, but there is a <p> that is not associated with any region. It's not clear why it is present and what effect it is intended to have in the IMSC-HRM algorithm.
Suggest deleting this <p> or associating it with a region, or if it's intended to have an effect, adding an XML comment explaining its unusual presence.
https://github.com/w3c/imsc-hrm-tests/blob/2393baeb431a624e09f7b23cf326de5e1c48da74/fail/dur003-fail.ttml#L14-L16
https://github.com/w3c/imsc-hrm-tests/blob/2393baeb431a624e09f7b23cf326de5e1c48da74/fail/ipd006-fail.ttml#L14-L16
https://github.com/w3c/imsc-hrm-tests/blob/2393baeb431a624e09f7b23cf326de5e1c48da74/pass/dur003-pass.ttml#L14-L16
https://github.com/w3c/imsc-hrm-tests/blob/2393baeb431a624e09f7b23cf326de5e1c48da74/pass/ipd006-pass.ttml#L14-L16
In all cases the document defines a region, so there is no default region, but there is a
<p>
that is not associated with any region. It's not clear why it is present and what effect it is intended to have in the IMSC-HRM algorithm.Suggest deleting this
<p>
or associating it with a region, or if it's intended to have an effect, adding an XML comment explaining its unusual presence.Is it there to produce an empty ISD, perhaps?