Function mark

docs/app/js/sanddance-app.js:123175–123181

(markdef, group6, index)

        return sceneToJSON(this.root, indent || 0);
    },
    mark (markdef, group6, index) {
        group6 = group6 || this.root.items[0];
        const mark = createMark(markdef, group6);
        group6.items[index] = mark;
        if (mark.zindex) mark.group.zdirty = true;
        return mark;
    }
};
function createMark(def2, group7) {
    const mark = {