When I search patents at espacenet.com I see that some patent documents have multiple priority numbers. For example WO2010054132 has 4 priority numbers. (see bibliographic data). What does this mean? Why there is more than 1 priority number?
Good question. I am unaware of any limit on the number of documents on which priority may be claimed.
Sometimes a patent application claims priority to an application that itself claims priority to another patent application.
For example, an inventor could file a provisional application. A non-provisional application could claim priority to the provisional. Later, the inventor could file a continuation-in-part that claims priority to both the provisional and non-provisional.
Here, WO2010054132 lists the following priority documents:
12/612,355 04.11.2009 US
61/112,080 06.11.2008 US
12/612,366 04.11.2009 US
12/612,349 04.11.2009 US
It looks like the earliest claim of priority is to a U.S. provisional filed on June 11, 2008. Three separate U.S. non-provisionals were subsequently filed on April 11, 2009.
12/612,366 appears to have been abandoned; the other non-provisionals appear to be pending.