In reply to Beyond OpenType: font format for the future speculation and brainstorming:
Somewhere out there in Typophile, I floated the idea of declarative fonts, i.e. of something like an XML font expression in which content and display are separated and in which glyph content is composed of extensible sets of labelled elements -- stems, arches, bowls, terminals, serifs -- arranged in relationship to each other. So, for instance, a lowercase roman a would be a particular arrangement of arch, stem, bowl, terminal and outstroke. The display -- weight, stroke type, transition type and proportion -- of each element would then be expressed as an attribute or through an external style sheet. A wide range of weights, widths and even styles of type could be produced from the same set of element relationships -- think of all the forms of roman a that can be described as having this basic relationship of parts --, and style attributes could be parameterised. One thing I like about this idea is that it introduces meaningful feature description into the font format, so that we actually have things that we can call serifs, rather than simply another kind of stem. This means we can apply changes to particular features across a range of glyphs while not affecting other features, e.g. modifying the weight of hairlines independently of the weight of serifs, or the weight of bowls independently of the weight of straight stems. [TT hinting enables similar independent control of labelled distances, which is one of the inspirations for this idea.]
Crucially, as an extensible system in which the font developer decides what features should be tagged as which elements, it is flexible enough to handle all the world's writing systems, and is not hampered by inherited paradigms. The tricky part, I reckon, will be transitions, the places where elements connect, which probably needs to presume a well defined rendering engine model, i.e. the piece of software responsible for interpreting the font declaration.
