Steps to Reproduce

run the select-all.zul
1. click the select-all checkbox
2. deselect 1 item.
the select-all checkbox is unchecked now.
3. click select-all

Current Result

all selections are cleared

Expected Result

select all items since the select-all checkbox is unchecked

Debug Information

if you do the steps :
1. select 1st item
2. select-all
The result is:

all items selected

the problem is:

Under the partially selected condition, clicking select-all checkbox might select all items or deselect all items which is not a clear behavior. Because current behavior works like a switch, it doesn't change its internal checked status according to all items' checked status. But the checkmark element will change between checked and unchecked. This is a conflict.

Proposed Spec.

1. When the select-all checkbox is unchecked, click it to select all items.
2. When the select-all checkbox is checked, click it to deselect all items.
3. only when all listitems are checked, the select-all checkbox is checked.

I have implemented a prototype in the attached js.