Consider using descType or represents for onScreen

[cconcolato]

Two options:

• use a special value of descType and the text content being ON, OFF, ...
• define a content descriptor with sub types like: audio.dialog.onscreen.on, audio.dialog.onscreen.off or audio.dialog.onscreen.on_off

[nigelmegitt]

I think it makes sense to do this in content descriptor.

[nigelmegitt]

@cconcolato in the absence of other suggestions, are you able to prepare a pull request removing OnScreen and adding content descriptor values? Let me know if you'd like any assistance.