[css-fonts] Conflicting tags in font-feature-settings

Hi,

It seems to me that the spec is not clear about what should happen if
conflicting tags are specified for font-feature-settings. For example, if
you set "font-feature-settings: 'hwid', 'twid', 'qwid'", only one of them
can be chosen, but it is not clear which would win in that case.

It seems to me all browsers have the same behavior (which isn't clear to me
what it is) but it isn't specified anywhere as far as I can see. Probably
this behavior should at least be mentioned somewhere?

- Xidorn