code: function keydown (event) {
      switch (event.keyCode) {
        case $mdConstant.KEY_CODE.DOWN_ARROW:
          if (ctrl.loading) return;
          event.stopPropagation();
          event.preventDefault();
          ctrl.index   = Math.min(ctrl.index + 1, ctrl.matches.length - 1);
          updateScroll();
          reportMessages(false, ReportType.Selected);
          break;
        case $mdConstant.KEY_CODE.UP_ARROW:
          if (ctrl.loading) return;
          event.stopPropagation();
          event.preventDefault();
          ctrl.index   = ctrl.index < 0 ? ctrl.matches.length - 1 : Math.max(0, ctrl.index - 1);
          updateScroll();
          reportMessages(false, ReportType.Selected);
          break;
        case $mdConstant.KEY_CODE.TAB:
          // If we hit tab, assume that we've left the list so it will close
          onListLeave();
  
          if (ctrl.hidden || ctrl.loading || ctrl.index < 0 || ctrl.matches.length < 1) return;
          select(ctrl.index);
          break;
        case $mdConstant.KEY_CODE.ENTER:
          if (ctrl.hidden || ctrl.loading || ctrl.index < 0 || ctrl.matches.length < 1) return;
          if (hasSelection()) return;
          event.stopPropagation();
          event.preventDefault();
          select(ctrl.index);
          break;
        case $mdConstant.KEY_CODE.ESCAPE:
          event.preventDefault(); // Prevent browser from always clearing input
          if (!shouldProcessEscape()) return;
          event.stopPropagation();
  
          clearSelectedItem();
          if ($scope.searchText && hasEscapeOption('clear')) {
            clearSearchText();
          }
  
          // Manually hide (needed for mdNotFound support)
          ctrl.hidden = true;
  
          if (hasEscapeOption('blur')) {
            // Force the component to blur if they hit escape
            doBlur(true);
          }
  
          break;
        default:
      }
    }
docs: Handles keyboard input.
  @param event