MPRIS provides a few optional features and we have to decide if we want to implement them:
void SetFullscreen(bool aFullscreen);
const char* DesktopEntry();
bool GetShuffle() const;
void SetShuffle(bool aShuffle);
Desktop Entry is the path to the .desktop file, I think.
The others are self explanatory. I guess we can only implement Fullscreen and Desktop Entry. Looping and Shuffle probably don't make sense for single media elements (versus a playlist).
Looping maybe, I don't know if HTML5's Media supports native looping?