apply_filters( 'relevanssi_searchform_dropdown_args', array $args )
This filter hook filters the parameters for wp_dropdown_categories() used to create category dropdowns in search forms.
Parameters
$args
(array) The parameter array, see wp_dropdown_categories() documentation.
More information
If you use the dropdown parameter in the search form shortcode to create a taxonomy dropdown, Relevanssi uses the WP function wp_dropdown_categories() to create the dropdown. This filter hook modifies the parameters of that function.
You can use this, for example, to change the order of the items in the dropdown (the orderby parameter) and control whether the “none” value is included and what the text is (show_option_none).