private string TryParseBinarySelector()
{
Token token = this.NextToken();
if (token == null)
return null;
if (token.Type == TokenType.Punctuation && token.Value == "|")
return token.Value;
if (token.Type == TokenType.Operator && IsBinarySelector(token.Value))
return token.Value;
this.PushToken(token);
return null;
}