§1. This goes right back to a curious feature of Inform 1, in 1993. To enable the use of player's holdalls, we must declare a constant RUCKSACK_CLASS to tell some code in WorldModelKit to use possessions with this Inter class as the rucksack pro tem. This is all a bit of a hack, and isn't really fully general: only the player has the benefit of a "player's holdall" (hence the name), with other actors oblivious.

void RTSpatial::compile_players_holdall(void) {
    if (K_players_holdall) {
        inter_name *iname = Hierarchy::find(RUCKSACK_CLASS_HL);
        Hierarchy::make_available(Emit::tree(), iname);
        Emit::named_iname_constant(iname, K_value,
            RTKinds::I6_classname(K_players_holdall));
    }
}

§2. Note that FoundEverywhere is a template routine existing to provide a common value of the I6 found_in property — common that is to all backdrops which are currently everywhere.

void RTSpatial::schema_everywhere(up_family *self, int task, unary_predicate *up,
    annotated_i6_schema *asch, kind *K) {
    switch(task) {
        case TEST_ATOM_TASK:
            Calculus::Schemas::modify(asch->schema, "BackdropEverywhere(*1)");
            break;
        case NOW_ATOM_TRUE_TASK:
            Calculus::Schemas::modify(asch->schema,
                "MoveObject(*1, FoundEverywhere); MoveFloatingObjects();");
            break;
        case NOW_ATOM_FALSE_TASK:
            StandardProblems::sentence_problem(Task::syntax_tree(),
                _p_(PM_CantChangeEverywhere),
                "not being 'everywhere' is not something which can be changed "
                "during play using 'now'",
                "because it's not exact enough about what needs to be done.");
            asch->schema = NULL; break;
    }
}

void RTSpatial::schema_nowhere(up_family *self, int task, unary_predicate *up,
    annotated_i6_schema *asch, kind *K) {
    switch(task) {
        case TEST_ATOM_TASK:
            Calculus::Schemas::modify(asch->schema, "LocationOf(*1) == nothing");
            break;
        case NOW_ATOM_TRUE_TASK:
            Calculus::Schemas::modify(asch->schema, "RemoveFromPlay(*1);");
            break;
        case NOW_ATOM_FALSE_TASK:
            Calculus::Schemas::modify(asch->schema, "MoveObject(*1, real_location, 1, false);");
            break;
    }
}

§3. In fact, at present "here" predicates are never included in propositions to be compiled, so this code is never used.

void RTSpatial::schema_here(up_family *self, int task, unary_predicate *up,
    annotated_i6_schema *asch, kind *K) {
    switch(task) {
        case TEST_ATOM_TASK:
            Calculus::Schemas::modify(asch->schema, "LocationOf(*1) == location");
            break;
        case NOW_ATOM_TRUE_TASK:
        case NOW_ATOM_FALSE_TASK:
            StandardProblems::sentence_problem(Task::syntax_tree(), _p_(BelievedImpossible),
                "being 'here' is not something which can be changed during play",
                "so it cannot be brought about or cancelled out with 'now'.");
            asch->schema = NULL; break;
    }
}