@property<EOL><INDENT>def global_symbols_in_children(self):<DEDENT>
result = set()<EOL>for child in self.children:<EOL><INDENT>result |= (<EOL>child.global_symbols |<EOL>child.global_symbols_in_children)<EOL><DEDENT>return result<EOL>
This is based on all children referenced symbols that have not
been declared.

The intended use case is to ban the symbols from being used as
remapped symbol values.