* ML bindings produced via Isar commands are stored within the Isar context (theory or proof). Consequently, commands like 'use' and 'ML' become thread-safe and work with undo as expected (concerning top-level bindings, not side-effects on global references). INCOMPATIBILITY, need to provide proper Isar context when invoking the compiler at runtime; really global bindings need to be given outside a theory. [Poly/ML 5.2 or later]
* Command 'ML_prf' is analogous to 'ML' but works within a proof context. Top-level ML bindings are stored within the proof context in a purely sequential fashion, disregarding the nested proof structure. ML bindings introduced by 'ML_prf' are discarded at the end of the proof. [Poly/ML 5.2 or later]