Update docs for forced and default flags
The description forced flag in particular describes behavior that never actually existed in any player implementation I'm aware of, and the default flag's purpose was unclear. The new text in the spec describes the existing in-the-wild usage of the forced flag (which matches the behavior of at least some existing players), along with an advisory usage for the default flag. The help text should be updated to reflect these. Something like this could work for forced:
--forced-track TID[:bool]
Sets the 'forced' flag for the given track (see section track IDs) if the optional argument bool is not present. Use this for tracks containing onscreen text or foreign-language dialogue.
Edited by rcombs