Text highlighter functiontionality

[stephan.zimmer]

Is anyone aware of a text highlighter functionality in emacs? I would
like to highlight (possibly non-connected) portions of text in a
buffer in such a way, that the highlighting persists within one emacs
session (i.e., when I change the buffer and return to it again, the
highlighting should still be there).

(To avoid confusion: I do not mean the selection of text, the intended
highlighting is just for a better orientation while reading the text.)

Stephan