Backward compatibility:

Process any previous version configuration file from the same minor version. For example, Infinispan release 4.2 should process configuration file produced for version 4.1 without any configuration file changes or any other adjustments. For configuration options present in 4.2, but not in 4.1 assume default values. However, Infinispan version 5.0 is not required to process configuration files from previous major versions, i.e 4.0...4.x.

Forward compatibility.

Do not process any forward version configuration file. For example, Infinispan release 4.1, give configuration file input from any succeeding versions (i.e 4.2...4.x, 5.x) would simply fail outright with proper error message.