Setup Open admin/webservice/forms.php and edit line 117, the line that adds a searchableselector for requiredcapability, and add the multiple option as follows: $mform->addElement('searchableselector', 'requiredcapability', get_string('requiredcapability', 'webservice'), $capabilitychoices, ['multiple' => true]); Purge your cache. In all browsers... Go to the add a new webservice screen ( admin/webservice/service.php?id=0 ) and click "Show more..." to display the search select box. Type 'ca' into the search box and observe that items are being filtered. Export jQuery to the global scope by entering the following into your JS console: require(['jquery'], function(jquery) { window.jQuery = jquery; }); Shift-select from mod/quiz:emailwarnoverdue to block/calendar_upcoming:addinstance, making a visual note of the number of visible options being selected. Check in your console that the collection of selected options is of the same size using jQuery: jQuery(':selected').length