zindex parameter fixed order, how automatically arrange in the correct order


help me please , my code…
var advancedTexture = BABYLON.GUI.AdvancedDynamicTexture.CreateFullscreenUI(“gui”);
var rect1=createRect(“rect1”);
advancedTexture.addControl(rect1);
rect1.linkWithMesh(…);
var rect2=createRect(“rect2”);
advancedTexture.addControl(rect2);
rect2.linkWithMesh(…);