> Here's my first attempt at a real-life use.

And here's a second attempt, which is a tentative patch for `eglot.el`.
This one does make use of the `before` argument, so it exercises more
the API.

The `eglot--virtual-pos-to-lsp-position` is not completely satisfactory,
since to compute the LSP position of the end of the chunk before it was
modified, I end up creating a temp buffer to insert the part of the text
that changed (to count its line+column, which is much easier in a buffer
than in a string).  That kinda sucks performancewise, but we do it at
most once per command rather than once per buffer-modification, so it
should be lost in the noise.

The upside is that we're insulated from the quirks of the
after/before-change-functions evidenced by the copious comments
referring to various bug reports.


        Stefan