sox.Sox instance to which the content
is to be written.
The name of the master you are defining; it must be a
valid XML name. You will use this name later in the
flow element to route the flow's content
to this master.
The function returns a token representing the open element.
Call one or more of the following functions to generate
the element or elements that specify which page master
to use in which situation, and then call the
.end() method on the token.