Given this input:

filedecl_beg = KW_FILEDECL_BEG, STRING, [ STRING ] ;

I run kgt with this command:

./kgt -l iso-ebnf -e bnf <input.ebnf

Actual output:

<filedecl_beg> ::= <KW_FILEDECL_BEG> <STRING>

Expected output, I cannot present here, but would expect that the second, optional STRING is present in the BNF output.