A layout is a simple pane that positions one or more child panes within itself according to a layout policy.
The layout description is an abstract description of the children of the layout, and each layout defines its format. Generally, the description is a list of either panes, slot names (where the name refers to a slot in the layout's interface containing a pane) or strings (where the string gets converted to a title-pane). Setting the layout description causes the layout to translate it, and then to layout the new children, adjusting the size of its parent if necessary.
A number of default layouts are provided which provide the majority of layout functionality that is needed. They are as follows:
A layout for one child.
Lays its children out in a row.
Lays its children out in a column.
Lays its children out in an n by m grid.