The multibuffer lets you refer to offsets inside of headers,
so it's possible to create a fold that appears non-empty,
but which spans zero characters in the underlying buffers.
Fold ranges are biased inward: the start is biased right, and
the end is biased left.
Because of these two things, it's possible to create a fold
that becomes "inverted" when you insert text at that position.
Max Brunsfeld
f898dc6dae