This is a C23 grammar extracted from n3096 C 23 draft written in a text format matching almost 1:1 the pdf version.

grammar

Less than 3 chars means token. For instance [ is a token. opt is reserved. "literals" are tokens for instance "goto". identifiers are productions.

See also https://github.com/cigix/cstdtohtml (Maybe the grammar extraction can be automated, pdf->txt->grammar.txt)