How to use CreateFunctionStmt's RETURN TABLE?

Hello Guys,

Lately, I saw this syntax in ./src/backend/parser/Gray.y as following!

CreateFunctionStmt:
CREATE opt_or_replace FUNCTION func_name func_args_with_defaults
RETURNS func_return createfunc_opt_list opt_definition
{
CreateFunctionStmt *n = makeNode(CreateFunctionStmt);
n->replace = $2;
n->funcname = $4;
n->parameters = $5;
n->returnType = $7;
n->options = $8;
n->withClause = $9;
$$ = (Node *)n;
}
| CREATE opt_or_replace FUNCTION func_name func_args_with_defaults
RETURNS TABLE '(' table_func_column_list ')' createfunc_opt_list opt_definition
{
CreateFunctionStmt *n = makeNode(CreateFunctionStmt);
n->replace = $2;
n->funcname = $4;
n->parameters = mergeTableFuncParameters($5, $9);
n->returnType = TableFuncTypeName($9);
n->returnType->location = @7;
n->options = $11;
n->withClause = $12;
$$ = (Node *)n;
}
| CREATE opt_or_replace FUNCTION func_name func_args_with_defaults
createfunc_opt_list opt_definition
{
CreateFunctionStmt *n = makeNode(CreateFunctionStmt);
n->replace = $2;
n->funcname = $4;
n->parameters = $5;
n->returnType = NULL;
n->options = $6;
n->withClause = $7;
$$ = (Node *)n;
}
;

I do not know how to use the second syntax:RETURNS TABLE '(' table_func_column_list ')' createfunc_opt_list opt_definition.

May someone help me to write a simple example of this syntax! Thank you very much. Looking forward for your help!