handleUserSearchSubmit = function(event) {
          var $this = $(this),
              targetId = $this.data('target'),
              controlsId = $this.data('controls'),
              templateId = $this.data('template'),
              prefix = $this.val() || $this.data('prefix') || '',
              startAt = $this.data('startAt') || null,
              endAt = $this.data('endAt') || null;

          event.preventDefault();

          userSearch(targetId, templateId, controlsId, prefix, startAt, endAt);
        }
Binds user search buttons, dropdowns, and input fields for searching all
active users currently in chat.