The ISC license contains similarities to both the MIT and simplified BSD licenses, the biggest difference being that language deemed unnecessary by the Berne Convention is omitted. Like the BSD license, the MIT license does not include an express patent license although some commentators state that the grant of rights covers all potential restrictions including patents. Both the BSD and the MIT licenses were drafted before the patentability of software was generally recognized under US law. The Apache License version 2.0 is a similarly permissive license that includes an explicit contributor's patent license. In the US, the MIT license contains the terms "use" and "sell" that are used in defining the rights of a patent holder in 35 U.S. Code section 154. This has been construed by some commentators as an implicit but badly-written license in the US to use any underlying patents.  , according to White Sources Software the MIT license was used in 27% of 4 million open source packages. , according to Black Duck Software and a 2015 blog from GitHub, the MIT license was the most popular free software license, with the GNU GPLv2 coming second in their sample of repositories. In June 2016 an analysis of the Fedora Project's packages revealed the MIT as most used license.