to go larking

Beyond type safety, OCaml has several features that closely interact with the garbage collector. These include weak references, finalisers, ephemerons, and lazy values, whose semantics will have to be preserved with the new GC so as to not break programs that use those features.

dig toxicity

The words jot and tittle in this passage refer to diacritic marks, that is, dashes, dots, or commas added to a letter to accentuate the pronunciation.