Compatibility of a particular license with a second license becomes an issue when a work that is licensed under the second license is to be integrated into a common work and to be compliantly copied and distributed under the first license.
Such compatibility is assumed, if
- compatibility with another license is explicitly ruled in a particular license, or
- the two licenses in question both do not contain a copyleft clause, or
- the second license does not contain a copyleft clause and does not impose an obligation that the first license does not allow to impose.

Incompatibility is assumed, if
- incompatibility with another license is explicitly ruled in a particular license, or
- one license imposes an obligation that the other license does not allow to impose, or
- the two licenses in question both contain a copyleft clause.

Statements on compatibility made elsewhere - even by the authors of a particular license text - are not considered for the decision whether a particular license pair is compatible or not.