Constants are included in sphinx output
As pointed out by Tim at the end of #25046 (closed) Sphinx is including our internal parser constants in its generated api docs...
HEADER_PARSER_FOR_LINE = {'valid-after': <function _parse at 0x7fba0426e488>, ...Marking this with the 'easy' keyword since it's a good one for newcomers to bite off. I suspect that if we mark these constants as private with a leading underscore Sphinx might skip it. If not we'll need to investigate Sphinx a little more to figure out how to exclude these.