internal/

Package constants declares the isnow library's sentinel error values — the four stable error codes every isnow implementation shares (specs/contracts/semantics.md in the grammar repo).

Package engine implements the isnow pattern engine: recognition of pattern source via the grammar repo's ANTLR-generated parser, the shorthand-ladder role assignment, compilation of every field term to a predicate, membership (Holds) over a broken-down instant, and occurrence derivation (Next/Prev) under the 100-year search horizon.