In MUDLibs that separate Inheritable and Clonable, a Program from which other programs may inherit. It may not be cloned, none of its functions can be directly called and it may have no variables nor any other kind of state. If it needs to be dynamically upgraded, it will be destroyed rather than recompiled in place, and it will be regenerated on demand from the new source. This is restrictive, but without it you may need to reboot the server to upgrade objects. Compare Clonable.