Steps to Reproduce

http://zkfiddle.org/sample/6eb1j5/1-caption-tabindex
run fiddle, click on 1st textbox, press tab.

Actual Result

caption receives focus, press again to focus 2nd textbox

Expected Result

focus should go directly on 2nd textbox, unless tabindex = 0 is defined on the caption

Debug Info

following ZK-2535, tabindex have a default value of 0 for caption
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/wgt/Caption.js#L23

Since caption is based on div, it would make more sense to have a default tabindex value of null / "" (empty string). If null / "" is not possible, -1 could also be a possible choice.

Root Cause

tabindex 0 is given as default for caption

Workaround

manually set tabindex -1 to the caption