2.2. Licensing Copyright owners have wide latitude in determining license terms. Common areas of restriction (or permission) include use, copying, distribution, and modification. As a concrete example, the GNU General Public License (GPL, commonly called the copyleft) explicitly does not limit use. It limits only "copying, distribution, and modification." Here is an example of free-software jargon with which you want to be familiar. In the free-software world, public domain is used almost exclusively in terms of ownership. In other circles, it is often applied to use, as well. Magazine articles that refer to the GPL as a "public-domain copyright" are clearly wrong because the GPL does not give ownership of the copyright to the public domain; articles that refer to it as a "public-domain license" are in one sense correct, because the GPL explicitly places no license restrictions on use. Free-software fanatics, however, often cringe at this use of public domain, and many believe it to be completely incorrect. Certain license restrictions may not be legal in certain localities. Most governing bodies prevent you from restricting what they consider fair use in a license agreement. For example, many European countries explicitly allow reverse engineering of software and hardware for certain purposes, license terms restricting such activities notwithstanding. For this reason, most license agreements include a separability clause something like the following one, from the GPL: If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. Most license agreements use less comprehensible language to say the same thing. Many people who attempt to write their own license terms without legal help write licenses with terms that have no legal force, and few of those licenses include a separability clause. If you wish to write your own license terms for your software, and if you care whether people comply with the license terms, have an intellectual-property lawyer vet your license terms. | 
