What is the xpcd executable / Darwin xpc(3) service

The first item in the search results for dialog com.apple.internetaccounts.xpc is http://ift.tt/1rKy84i, which complains that "[e]very 10-15 minutes the following prompt pops up on the screen" (img-1), and is how I learned of the Darwin XPC service.

The documentation I have so far (from an up-to-date Mavericks machine):

1. The Darwin xpc(3) manpage, which names 12 other man pages, of which none are 'xpcd' and one does not actually have a man page (i.e. man 3 xpc_abort gives an error). (You apparently need Xcode for man 3 xpc to give you the page at your CLI;)


2. ActivityMonitor.app shows three PIDs named 'xpcd', which I think is probably part of the XPC service. The three PIDs are run with UIDs 'root', '_security' and whoami;


3. No results for man xpcd


4. 
   

   mdfind xpcd gives:

   
   

   
   helen:~ stewart$ mdfind xpcd
   /System/Library/Sandbox/Profiles/com.apple.xpcd.sb
   /System/Library/LaunchDaemons/com.apple.xpcd.plist
   /usr/libexec/xpcd
   
   

I want to know more about this service, in particular, I want to know:

1. What command-line arguments does /usr/libexec/xpcd take?


2. How do I determine what the XPC service is doing? When does it ask for items from the Keychain?


3. Is xpcd properly documented anywhere?

(img-1): The image link from that discussions.apple.com discussion page is broken, but presumably the same as twitter-dialog-xpc.png: