Rework the information on section lengths.
Review Request #11691 — Created June 30, 2021 and submitted
This clarifies the
length=option for sections. It explains when a
length is required and when it isn't, how a length is calculated, and
the rationale for the lengths.
Lengths are no longer optional. Content sections (preambles, metadata,
diffs) now require it.
Some lengths in examples have been fixed to be accurate for the
Built the docs and read through the affected sections.
Tested all lengths in the examples to make sure they were now correct.