[Checkins] [zopefoundation/Zope] f2132c: add test for `CONTEXTS`; restore `CONTEXTS` relate...

[Dieter Maurer]

  Branch: refs/heads/lost_variables#860
  Home:   https://github.com/zopefoundation/Zope
  Commit: f2132c7e8ddf9ec55e4e12f1ce4c8b688f6c29cb
      https://github.com/zopefoundation/Zope/commit/f2132c7e8ddf9ec55e4e12f1ce4c8b688f6c29cb
  Author: dieter <dieter at handshake.de>
  Date:   2020-07-05 (Sun, 05 Jul 2020)

  Changed paths:
    M CHANGES.rst
    M docs/zopebook/AppendixC.rst
    M src/Products/PageTemplates/tests/testVariables.py

  Log Message:
  -----------
  add test for `CONTEXTS`; restore `CONTEXTS` related documentation (improved)