code: function optimize (root, options) {
    if (!root) { return }
    isStaticKey = genStaticKeysCached(options.staticKeys || '');
    isPlatformReservedTag = options.isReservedTag || no;
    // first pass: mark all non-static nodes.
    markStatic(root);
    // second pass: mark static roots.
    markStaticRoots(root, false);
  }
docs: Goal of the optimizer: walk the generated template AST tree
  and detect sub-trees that are purely static, i.e. parts of
  the DOM that never needs to change.
  
  Once we detect these sub-trees, we can:
  
  1. Hoist them into constants, so that we no longer need to
  create fresh nodes for them on each re-render;
  2. Completely skip them in the patching process.