bug#47711: [PATCH VERSION 2] Add new `completion-filter-completions` API and deferred highlighting

[Dmitry Gutov]

On 14.08.2021 10:01, Eli Zaretskii wrote:

> Just to make sure we are on the same page: adding a text property to a
> string doesn't mutate a string.  Lisp programs that process these
> strings will not necessarily see any difference, and displaying those
> strings will also not show any difference if the property is not
> related to display.  So the assumption that seems to be made here,
> that adding a property is the same as mutating a string, is IMO
> inaccurate if not incorrect.

This is nonsense.

A program won't necessarily see a difference in *any* changed value, as 
long as some part of it stays the same.

I can zero out the tail of a string, and have a program that only looks 
at its first few characters. It wouldn't mean that a string hasn't changed.