Multiple simultaneous RehearsalMarks, tunable output per score, grace synchronized [obsolete in 2.23]

An alternate engaver for RehearsalMarks with many features, e.g.

This snippet is obsolete starting from LilyPond version 2.23.14, which introduces the \textMark and \textEndMark commands. There is no restriction similar to rehearsal marks: there can be several text marks at the same moment.