A page master is a master template that is used to generate a page, and it specifies the actual layout of the page. You can use a page master whenever you want to in a document. Each page master has a unique name.
In the current XSL specification, there is only one kind of page master, the fo:simple-page-master object; in the future, the XSL specification may support additional page masters. You use the fo:simple-page-master object to generate pages and define the geometry of the page.
To set the overall geometry of the page, you can use these properties of the fo:simple-page-master object:
Common margin properties for blocks: margin-top, margin-bottom, margin-left, margin-right, space-before, space-after ...