# note: this might be incomplete, mostly an example
root        ::= en-char+ ([ \t\n] en-char+)*
en-char     ::= letter | digit | punctuation
letter      ::= [a-zA-Z]
digit       ::= [0-9]
punctuation ::= [!"#$%&'()*+,-./:;<=>?@[\\\]^_`{|}~]