[development] implementing #format

[Daniel F. Kudwien]

> I was rather thinking about #format being too generic and 
> possibly misleading / conflicting for efforts to get email, 
> number, etc. type fields, which would probably need a similar 
> meta-mechanism for format limiting / specification. Anyway, 
> if this comes significantly sooner, then the patch coming 
> later needs to bother with this :P I am just trying to 
> solicit some initial feedback, so that the keywords do not 
> need to be modified later.

Good point, '#format' would indeed be ambigious.  '#filter_format', '#filter
format', or '#filter-format' would be more appropriate, IMHO.

If we tie input formats to form elements, we should also implement some
logic to let filters know about which field is actually filtered, and, to
which object the field belongs.  Most filters suffer from not knowing
anything about the context of the filtered content.  That information is
very valuable, for example to generate different output for different
fields, or to access certain other values of a node object while filtering a
field of it.

Daniel