Alternation : 
    CSN1String  '|'  CSN1String
|   CSN1String  'or'  CSN1String
|   CSN1String  '!'  CSN1String
            

The '|' and 'or' operators are equivalent.

An Alternation matches any string that is matched by either of the operands. The '!' operator is similar to the other operators except that a match on the right hand operand is counted as an error.