An operator is represented by a string of special characters other than ?, _, braces, brackets, parentheses or quotes, possibly followed by a suffix consisting of the back-quote ` followed by a string eligible to be an atomic term. It is permissible for an operator to have no suffix; a suffix by itself is also a permissible operator; the empty string is not an operator.
An operator beginning with a caret , other than the one-character operator itself, is an operator variable. The syntactical privileges of operator variables are the same as those of other operators.