GitLab

On request of @jburr to make this easier to understand and teach for
beginners.  Note that this involved a fair amount of whitespace
changes to make the for-body indentation consistent with the rest of
each file.

Originally I had tried sweeping/cherry-picking this from 21.2, but
with all the three-way merges and commits that involve other
packages/directories that was rather painful, so this is now just a
direct copy from the current state in 21.2.