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.