What is the OSX ruler clipboard? I ran man pbcopy which listed the flag -pboard with options {general | ruler | find | font}.  I understand what the general, find, and font clipboards are, but I can't find any documentation on what use the ruler clipboard has.
The ruler pasteboard, or NSRulerPboard at the programming level, is:


  The pasteboard that holds information about paragraph formats in support of the Copy Ruler and Paste Ruler commands that may be implemented in a text editor.


You can read much more about the Pasteboard here.