A number of operations and options introduced in the early versions of TikZ are no longer documented but are still used and useful.
For example, the syntax used in this question Specifying the point via "intersection of" in TikZ - a problem which is :
(intersection of a--b and c--d)
is no longer documented since version 3.0.
Ulrike Fischer asks the same question to Percusse in a comment on Feb 1 '16 at 9:19, I quote:
@percusse: Is this use of intersection of X and Y documented somewhere? I can find the documentation of the library and named path but nothing else.
Old code can be found everywhere on the net and the latest manuals do not always explain the syntax used.
The purpose of this question is to archive and to be able to quickly find old manuals.
Translated from french with www.DeepL.com/Translator (free version)