If you're talking about the curly braces after the backtick in the syntax diagram for operators, I think that's just a way to escape those special characters so

If you're talking about the curly braces after the backtick in the syntax diagram for operators, I think that's just a way to escape those special characters so you can use them in operator names. It would be the same as escaping a double quotation mark in a string literal with a backslash, i.e: "\""