Would you add a class to indicate the panel is open at the panel level?

I'm using a caret indicator in the panel-title like so:

.panel-title > a:before { 
  content: $fa-var-angle-right;
  font: normal normal normal 14px/1 FontAwesome; }

.panel-open .panel-title > a:before {
  content: $fa-var-angle-down; }

Adding a class like panel-open on the panel div would allow me to just go like

<accordion-group is-open="thisDrawer.open">

instead of

<accordion-group is-open="thisDrawer.open" ng-class="{'panel-open': thisDrawer.open}">