Layout elements define an arrangement of content areas. For example you
can define a layout that has three vertical columns where the left and right
hand columns have fixed with and the middle column flexes with screen width.
Layouts have the following features:
Layouts consist of one or more zones where each zone can contain a component,
template, static html, region, or layout.
The zones of the layout can be nested in containers to define how the zones
are positioned relative to each other on the page.
The layout can define the default content of each zone in the layout. This
can be overriden in each place where the layout is used. For example you
can define a page layout that is used on every page and defines the page
header and footer. On every page where this layout is used the page can
define different content for the main body of the page.