code: function addChildSpacing(wt) {
      var d = 0, modsumdelta = 0;                                    
      for (var i = 0; i < wt.num_children; i++) {                                  
        d += wt.children[i].shift;                                               
        modsumdelta += d + wt.children[i].change;                                
        wt.children[i].mod += modsumdelta;                                       
      }                                                                 
    }
docs: Process change and shift to add intermediate spacing to mod.