Question about setPaperSource

Dear All
As a requirement, I need to switch between printer trays while printing a document. I used QPrinter's setPaperSource, but it seems that for different printer devices, the value which should be set as the argument of the so called function is different. QPrinter::PaperSource supports 13 or 14 values as possible paper sources. When I query the device using supportedPaperSources function, I get a list of values which are greater than QPrinter::PaperSource values. Is it possible to use these values as the argument in setPaperSource? By the way, the description of supportedPaperSources says something like what follows which does not make sense:
Returns the supported paper sizes for this printer.
Is this OK? I use Qt 4.6.2

Warm Regards
Ali