Open Source licenses always permit changing or expanding existing material or combining it with other components. In some cases, the license imposes obligations on the resulting modified work. In particular it might be required to license the modified work under the original license. Such a clause in an Open Source license is called "copyleft". The scope of a copyleft clause, i.e. which modifications must be licensed under the original license, depends on the individual license. Some licenses state the scope of the copyleft clause explicitly, i.e. the file-based copyleft of the MPL-2.0 or the exemption of linked components from copyleft of the LGPL-2.1. For others it is open to interpretation. To reflect these differences in the canonical language of the checklists, a copyleft clause appears twice in a checklist.
- The actual obligations resulting from a copyleft clause are listed under the condition "IF Software modification" without specifying which types of modifications are affected.
- If applicable, the section "Copyleft clause" contains the reference to the respective wording in the license text to help interpret the scope of the copyleft.