How do u create a block when the form is initialized via XML

I have a form that gets its stucture from the server. However i have some difficulties implementing the block item. Can you please point me some example that clearly shows how to create the form item via xml load?

Here you can find a docs with the xml examples:

<item type="block" name="data" label="Welcome"> <item type="input" name="name" label="Login" position="label-top"/> <item type="password" name="pass" label="Password" position="label-top"/> <item type="button" name="save" value="Proceed"/> </item>

i don’t see the block item!?
i see combo, multiselect and so on but i clearly ask about the block item

block is similar to the fieldset.
There is the detailed definition only for the specific items.