The FormBinding doesn't handle collection inside currently,
There are 3 issues need to be handle in the case.
1.The update to tag should store in form and update later.
2.The add new tag should store in form and create(how could I create a user's bean?) later
3.The delete old tag should store in form and delete later.
for 1. could consider to use nested form. such as.
<grid form="@id('fx') @load(vm.currentItem) @save(vm.currentItem, before='save')">
<listitem form="@id('fx2') @load(each) @save(each, before='save')">
<textbox value="@bind(fx2.value)" />
However, for 2,3, there are no good solution yet for just using form-binding. we need a new (not-just) form-binding.