Have you looked at the text widget in Tk? It has markers and regions and allows arbitrary labeling of (possibly discontiguous) regions of text. I think it's pretty cool, and might have some of the fundimental features you're looking for.

In reply to Re: Implementing (elisp-like) buffers in Perl 6: how to do buffer-localisation of arbitrary package variables? by John M. Dlugosz
in thread Implementing (elisp-like) buffers in Perl 6: how to do buffer-localisation of arbitrary package variables? by jonadab

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