[pygtk] Help with print preview

[Richard Taylor]

Hi

I am a little confused about how the print preview callback of PrintOperation 
is meant to work.

The docs say:

"""
The "preview" signal is emitted when a preview is requested from the native 
dialog. If you handle this you must set the cairo context on the printing 
context.

If you don't override this, a default implementation using an external viewer 
will be used.
""

Firstly, can anyone explain what "set the cairo context on the printing 
context." means?

Secondly, does anyone know what "external viewer" will be used?

I am struggling a little with this because I can't find any good examples of 
python apps using the PrintOpertion classes.

Many thanks,

Richard