form-layout lays its children out in a form.
The gap between rows in the form.
The adjustment made to the rows.
The gap between the two columns.
The adjustment made to the left column.
The form layout lays its children out in two columns, where the children in the left column (which are usually titles) are right adjusted while the children in the right column are left adjusted.
This class has been superseded by grid-layout, and will probably be removed at some point in the future. The examples below demonstrate the use of grid layouts as an alternative to forms.
(setq children (list
:text "Press Me")
:items '(1 2 3))))
:x-adjust '(:right :left)
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015