0. PREAMBLE
The purpose of this Licence 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 Licence 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 Licence 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 Licence, which is a copyleft licence designed for free software.
We have designed this Licence 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 Licence 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 Licence principally for works whose purpose is instruction or reference.