Allow (more?) properties, such as textAnchor, dx, dy, to be specified as functions of data (but not bound to scales)?

[Fil]

For text marks I'd like to be able to specify fontWeight (as a constant) ((maybe accept also font-weight?)).

[Fil]

Another use case in the Marimekko chart.

[mbostock]

I feel this issue should be broken down:

• The Text mark should support more constant properties such as fontWeight. (Easy.)
• Should some of the existing constant properties (e.g., textAnchor) support being data-driven? (Medium.)
• Should any constant property be expressible, somehow, as a data-driven channel if desired? (Hard.)

My working assumption is that Marks currently get to decide whether a property is a constant or a channel (or either, e.g., with maybeColor), so if a given Mark doesn’t expose what you want, we either need to change the Mark definition to make it more flexible, or extend the Mark to create a new one. I do think it ends up being simpler if a Mark implementation can declare something as a constant property, rather than needing to support every property as possibly being data-driven. Also, even for constant properties, you can make things somewhat data-driven by declaring multiple marks (as in the Marimekko example) and possibly filtering the data.

[mbostock]

This issue should be broken down as suggested.

[Fil]

broken into #173 #174 #175