_fnGetInitialFocus = function (context) {
                var that = context;
                assert(!!that, "No ToolPopup instance given for _fnGetInitialFocus");

                // if there is an initial focus it was already set to the Popup onBeforeRendering
                if (!that._bFocusSet) {
                    _fnGetNewFocusElement(that);
                } else {
                    that._sInitialFocusId = that.oPopup._sInitialFocusId;
                }

                return that._sInitialFocusId;
            }
Checks if the ToolPopup already has a tabbable element.
If not, it's checked whether the fake-element should be used or if there is an element that could be focused instead.

@param {sap.ui.ux3.ToolPopup} context to get/set instance values
@returns {string} _sInitialFocusId that has been determined here
@private