I stripped down the project to isolate the problem, and I identified it that way.
I had a numbered list item that contained a double-colon literal block that was indented only as far as the list item's text, like this:
2. Set up the... directory::
$ A Linux command
$ Another Linux command
$ And ANOTHER Linux command
$ etc.
When I indented the literal block further, the problem went away.
I was misled by two things:
The message does not point to the first line in the literal block, but to some apparently random line within it. In the case above, it pointed to the fifth line (out of eight) in the block!
In most cases this form of indention, although incorrect, works just fine.
Isolating the problem is a brute-force method of solving it, but is often effective when deduction fails. I'll keep that in mind in the future.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…