The |find filter is used to check the existence of a given value in the array to which it is applied:
[(#GET{my_array}|find{the_value}|oui) This text will display if the value of "the_value" is included in the "my_array" member values.]
If #GET{my_array} is not a PHP type table/array, the tag being filtered by |find will not return anything.
See also : the filter |in_any