I'd like to find all occurrences of
== in a buffer and overlay them with Unicode
≡, keeping width of two chars and centered in the space.
I know about replacing text visual representation:
(put-text-property 1 10 'display "replacement")
about keeping known width
(put-text-property 1 10 'display '(space :width (119)))
I do not know how to put this together and keep it centered.