All forms contain a root (parent) subform. In the Hierarchy palette, the root subform (form1) is displayed as the top-level node with the default page subform (untitled Subform) appearing as a child node below the root subform.
LiveCycle Designer ES automatically adds to every page a default subform that covers the whole page, and corresponds in size and position to the default content area on the master page. Any subforms that you subsequently add to the pages are nested in and appear below the default page subform in the Hierarchy palette.
Livecycle working with subforms.32.4.1 Default subforms
In the Hierarchy palette, each subform is represented by a node, and the objects wrapped in a subform are displayed under the subform node. The children of the subform do not inherit changes made on the subform level; the properties of each object must be defined individually.
Livecycle working with subforms.32.4.2 Default subforms
If you look at the Purchase Order sample, the root subform, form1, is shown as the top-level node with the default page subform, purchaseOrder, appearing below as a child of the root subform. The other subforms used to wrap objects on the page (header, detailHeader, detail, and total) are nested under the page subform. In the Hierarchy palette, each subform is represented by a node, and the objects wrapped in a subform are displayed under each node.
See also 

Default subforms