This tab can be used to modify the layout of the currently edited alternative form. If you check the Use custom form layout check-box, a text area along with a standard WYSIWYG editor will be displayed, enabling you to create a custom form layout. Clicking the Generate table layout button above the editor will generate a default table layout containing all visible fields defined on the Fields tab.

 

Detailed information the Alternative forms module is located in Developer's Guide -> Modules -> Alternative forms.