🔡:={🅰️|🅱️}

#ebnf #production rule example #syntax definition #grammar example #formal language notation #concrete syntax

✍️\d{3}-\d{4}📞

#regex #regexp #regular expression #writing patterns #character classes #text processing #syntax definition #data extraction #phone number format

🖋️📜➡️🌳

#yacc #grammar specification #bnf #syntax definition #language rules #compiler construction