code: function WrappedTree(w, h, y, c = []) {
    const me = this;
      // size
    me.w = w || 0;
    me.h = h || 0;
  
      // position
    me.y = y || 0;
    me.x = 0;
  
      // children
    me.c = c || [];
    me.cs = c.length;
  
      // modified
    me.prelim = 0;
    me.mod = 0;
    me.shift = 0;
    me.change = 0;
  
      // left/right tree
    me.tl = null;
    me.tr = null;
  
      // extreme left/right tree
    me.el = null;
    me.er = null;
  
      // modified left/right tree
    me.msel = 0;
    me.mser = 0;
  }
docs: wrap tree node