Org-mode allows to skip the argument of a code block header argument if
it's toggling a value. Argument-less headers are now recognized,
avoiding weird parsing errors.
The fixes are not exactly pretty, but neither is the code that was
fixed. So I guess it's about par for the course. However, a rewrite of
the header parsing code wouldn't hurt in the long run.
Thanks to @jo-tham for filing the bug report.
This fixes#2269.
27a8603278