Label Restructuring

[IMP1]

Marksets on an edge's label are not maintainable. At all. This seems bad to me, as the label's value is maintainable, using a variable. Should there be a convenient way to reference a markset? This seems like a lot of additional complexity (is a markset its own type? is it an array of marks, which are their own type?).

Perhaps marksets should be gotten rid of. Is a single label value enough? Another type (colour or style or something) could be added.

Maybe it needs to be a list of values. But then the same problem arises, there's no way to keep the rest-of-the-list of an edge's label. Only whichever variable you've matched on.

What's the use case for multiple values?
I think I can see a use-case for having both a value, and some styling/debugging information, or some marker of a 'head' node or edge. And maybe the current markset is fine for that goal.