Looks like it's converting the name to lowercase, which is correct for ordinary grammarterms that are only capitalized when they appear at the start of a sentence, but is incorrect for these regex nonterminals whose names include real capital letters.
E.g. in http://eel.is/c++draft/re.grammar#4
Looks like it's converting the name to lowercase, which is correct for ordinary grammarterms that are only capitalized when they appear at the start of a sentence, but is incorrect for these regex nonterminals whose names include real capital letters.