So the default themes are a bit weak and there is no way to control it from the field configuration page.

Let's have 2 new dropdown menus, input and output theme, for each of the field types.

There will have to be an internal map of which theme functions can support which input and output types.

We'll keep things friendly for the PHP themers as well:

output

  1. a top level theme function that can be overridden with the effect of ignoring the output theme menu entirely
  2. theme functions for the individual items on the output menu
  3. facility for adding themes to the output menu by registering a theme function by name

input

  1. facility for adding forms to the input menu by registering a form-generating callback