The purpose of this License is to make a manual, textbook, + or other written document "free" in the sense of freedom: to + assure everyone the effective freedom to copy and redistribute it, + with or without modifying it, either commercially or + noncommercially. Secondarily, this License preserves for the + author and publisher a way to get credit for their work, while not + being considered responsible for modifications made by + others.
This License is a kind of "copyleft", which means that + derivative works of the document must themselves be free in the + same sense. It complements the GNU General Public License, which + is a copyleft license designed for free software.
We have designed this License in order to use it for manuals + for free software, because free software needs free documentation: + a free program should come with manuals providing the same + freedoms that the software does. But this License is not limited + to software manuals; it can be used for any textual work, + regardless of subject matter or whether it is published as a + printed book. We recommend this License principally for works + whose purpose is instruction or reference.