<selector> ::= "@" <type> "[" <props> "]"
<type> ::= "a" | "r" | "p" | "e" | "s"
<props> ::= (<prop> ",")* <prop>
<prop> ::= <prop_key> "=" <prop_val>
<prop_key> ::= <alpha>* (<alpha> | <digit> | "_")
<prop_val> ::= <prop_int> | <prop_float> | <prop_nbt> | <prop_str>
<prop_int> ::= "0" | <sign> [1-9]? <digits>
<prop_float> ::= "0" | "0.0" | "0." "0"+ | <sign> [1-9]? <digits> ("." <digit>* [1-9])
<prop_nbt> ::= "{}"
<prop_str> ::= "!"? <alpha>*
<alpha> ::= [A-Z] | [a-z]
<digit> ::= [0-9]
<digits> ::= <digit>+
<sign> ::= "-"?