Internet Explorer users will get no benefit from doc-subtitle;
NVDA with Firefox works well;
VoiceOver on iOS will also claim they are all heading level 2, and offers no context from aria-roledescription;
TalkBack with Chrome does not assign a level, but if you nest doc-subtitle within a native <h#> the content will be hidden.
TalkBack with Firefox works well.
Adrian provides some helpful alternatives depending on your goal.

#programming #development

I Was Wrong About How to Create Accessible Subtitles
1.15 GEEK