- compound-variable-separator #!optional stringparameter
A string representing the separator for request variable names bound to compound data types (vectors, alists, hash-tables). The default value is ".".
For example, if (compound-variable-separator) yields "." and the query string is ?foo.A=0&foo.B=1, if you bind it as an alist, you'll get ((A . 0) (B . 1)). If you want the same behavior, but for query string with variables like ?foo_A=0&foo_B=1, you can set compound-variable-separator to "_".