- parameters
- anchor not a part?
- guide_mode instead of guide_type
- shouldn't a non-consrtained input guide have a different mode than a
constrained input guide? I wonder if input/non-input and fixed/adjustable
are actually orthogonal after all.
- data_sequence: how collections of arbitrary application data are going to
be handled has to be decided yet (this is not really an mrl issue).
- some kind of type for part name for the mrl is needed.
- conditionals' where: rather than pointer to part, pointer to parent
and name of part.
Pablo