[Fontconfig] Regularizing contains operator semantics

[Keith Packard]

Around 1 o'clock on Jul 12, Ambrose Li wrote:

> With the current version of fontconfig (and gtk2), it is getting
> difficult to get X applications to let me use, for example, a
> Japanese font for traditional Chinese, even if the font is
> perfectly fine for the task I do, because the application will
> believe the fontconfig notion of "support" for my locale, and
> filter out all the "unsupported" fonts.

Perhaps this is not a problem with fontconfig, but rather with how 
applications interpret it's interface in presenting fonts.  Fontconfig 
always places application specified families higher in precedence than 
fonts selected strictly through language coverage concerns, so you should 
be able to specify any font family by name and have it work in whatever 
locale you are using.

The notion of language support is designed precisely for the case where 
no specified font family is available on the system and a 'fall-back' to 
available fonts is required; choosing one with 'support' for the language 
ensures that multiple fonts won't be needed.  Font substitution is a hard 
problem, and this language coverage mechanism has made a positive change 
in many environments on the resulting presentation of documents.

> I think it counter-productive to put so much trust in the mechanical notion
> of "complete code space coverage".

Perhaps we need to create better interfaces for applications to help 
clarify where language coverage is intended to be used.  Suggestions on 
what should be done are welcome.

-keith