A compiled <assign> executable-content node (spec 5.4, 5.9.2) - the interned counterpart to Statifier.Document.Assign.

location is the raw, uncompiled SCXML location attribute (a path expression such as "foo.bar.baz" or "items[0]") - it cannot be resolved any earlier than execute/2 even in principle, since a bracket key such as items[i] reads i against the pre-assignment datamodel. node_location is this node's own Statifier.Parser.Location span - named apart from location for exactly the reason Statifier.Document.Assign's moduledoc gives, so the raw path string and the element's own span are never confused. location_location is attribute_locations[:location]'s value span (the location attribute's own span, nil only if somehow never written - spec 5.4.2 requires it), following expr_location's "caller's choice" convention every other compiled node uses.

value is the value-source ladder's compiled result: {:static, nil} when <assign> writes no expr (Phase 3 adds the child-content rungs), otherwise Machine.expr() or - Decision 6's deferral, the same mechanism Statifier.Machine.Data.value already uses for <data expr> - {:invalid, Compiler.Error.t()} when expr failed to compile. expr_location is nil exactly when expr was never written.

Its Statifier.ExecutableContent implementation lives right below the struct: this file is the whole node, top to bottom, with no dispatcher anywhere else in the tree. The location-resolution, system-variable, root-existence, and write mechanics (spec 5.4.2/5.9.2/5.10) live in Statifier.Interpreter.Datamodel.write_location/4 - extracted so idlocation (6.4.1) and the empty-<finalize> auto-assign (6.5) can call the same mechanics without duplicating them here. A successful write also produces one {:datamodel_change, _} core effect - the one place a <assign>'s written location and value reach a consumer.