[githubalphapapa]

Buffers and strings with range-indexed metadata is also how Emacs's text properties work. For example, this shows the print syntax for strings with properties:

    (concat (propertize "foo"
                        'face '(:weight bold))
            " "
            (propertize "bar"
                        'link "http://bar"))
    ;;=> #("foo bar" 0 3 (face (:weight bold)) 4 7 (link "http://bar"))