On Tue, Nov 30, 2021 at 9:32 PM Eli Zaretskii <eliz@gnu.org> wrote:

> [...] a display spec that would enlarge the pixel width of every character
> with that display property by some number of pixels.  The display spec can
> be called char-width.
>

I know that the two great problems are naming, cache invalidation, and
off-by-one errors, but in case it helps: if I understand the concept
correctly, it's very close to what typesetting calls "tracking".

Hope that helps,
~Chad