Function is_atext 

pub fn is_atext(byte: u8) -> bool

Printable US-ASCII characters not including specials. Used for atoms.

atext = ALPHA / DIGIT / “!” / “#” / “$” / “%” / “&” / “’” / “*” / “+” / “-” / “/” / “=” / “?” / “^” / “_” / “`” / “{” / “|” / “}” / “~”