I'm not sure if they are context-free, but talks about Parseable Expression Grammars, specifically Lua's LPeg, implies they might be. Conceptually, PEGs are to

I'm not sure if they are context-free, but talks about Parseable Expression Grammars, specifically Lua's LPeg, implies they might be. Conceptually, PEGs are to Context Free Grammars as RegEx is to Regular Expressions. You can find multiple short email validation snippets using Lua LPeg pretty easily, but this is from the Lua creator's talk about LPeg which includes a part about proper RFC822 validation and how complicated it is for regex, but can be concisely done with PEGs. http://program-transformation.org/pub/WGLD/Austin2012/Roberto.pdf http://program-transformation.org/pub/WGLD/Austin2012/Robert... Here is the entire PEG slide. (Looks CFG-ish to me.) address <- mailbox / group group <- phrase ":" mailboxes? ";" phrase <- word ("," word?)* mailboxes <- mailbox ("," mailbox?)* mailbox <- addr_spec / phrase route_addr route_addr <- "<" route? addr_spec ">" route <- ("@" domain) ("," ("@" domain)?)* ":" addr_spec <- local_part "@" domain local_part <- word ("." word)* domain <- sub_domain ("." sub_domain)* sub_domain <- domain_ref / domain_literal domain_ref <- atom domain_literal <- "[" ([^][] / "\" .)* "]" word <- atom / quoted_string atom <- [^] %c()<>@,;:\".[]+ quoted_string <- '"' ([^"\%nl] / "\" .)* '"'