diff --git a/src/script_opt/DefPoint.h b/src/script_opt/DefPoint.h
new file mode 100644
index 0000000000..e231d72dc3
--- /dev/null
+++ b/src/script_opt/DefPoint.h
@@ -0,0 +1,105 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#pragma once
+
+#include "zeek/Expr.h"
+#include "zeek/Func.h"
+#include "zeek/Stmt.h"
+
+namespace zeek::detail {
+
+// A DefinitionPoint is a location where a variable, or possibly a record
+// field, is defined (i.e., assigned to).  The class tracks the type of
+// definition (a statement, inside an expression, an aggregate passed to
+// a function or hook, or at the start of a function).
+
+typedef enum {
+	// Used to capture the notion "the variable may have no definition
+	// at this point" (or "has no definition", depending on whether we're
+	// concerned with minimal or maximal RDs).
+	NO_DEF,
+
+	// Assigned at the given statement.
+	STMT_DEF,
+
+	// The following includes assignments, +=, vec+=, $, ?$ ...
+	// ... plus names (for implicit creation of records upon
+	// seeing use) and calls (for aggregates).
+	//
+	// Note that ?$ does not in fact create a definition.  We include
+	// it as a heuristic meaning "code after this point can assume
+	// that the given record field is defined".  The heuristic can
+	// fail if the ?$ predicate is ultimately negated, something that
+	// we don't try to identify.  Basically, the idea is that if the
+	// script writer is cognizant of needing to check for the existence
+	// of a field, most likely they got the check correct.  Any errors
+	// we make in this regard only lead to mistakes in identify usage
+	// problems, not in actual run-time execution.
+	EXPR_DEF,
+
+	// The variable is assigned when the function begins executing,
+	// either through an explicit initialization for a local, or because
+	// it's a function parameter.
+	FUNC_DEF,
+
+} DefPointType;
+
+class DefinitionPoint {
+public:
+	DefinitionPoint()
+		{
+		o = nullptr;
+		t = NO_DEF;
+		}
+
+	DefinitionPoint(const Stmt* s)
+		{
+		o = s;
+		t = STMT_DEF;
+		}
+
+	DefinitionPoint(const Expr* e)
+		{
+		o = e;
+		t = EXPR_DEF;
+		}
+
+	DefinitionPoint(const Func* f)
+		{
+		o = f;
+		t = FUNC_DEF;
+		}
+
+	DefPointType Tag() const	{ return t; }
+
+	const Obj* OpaqueVal() const	{ return o; }
+
+	const Stmt* StmtVal() const
+		{ 
+		ASSERT(t == STMT_DEF);
+		return (const Stmt*) o;
+		}
+
+	const Expr* ExprVal() const
+		{
+		ASSERT(t == EXPR_DEF);
+		return (const Expr*) o;
+		}
+
+	const Func* FuncVal() const
+		{
+		ASSERT(t == FUNC_DEF);
+		return (const Func*) o;
+		}
+
+	bool SameAs(const DefinitionPoint& dp) const
+		{
+		return dp.Tag() == Tag() && dp.OpaqueVal() == OpaqueVal();
+		}
+
+protected:
+	DefPointType t;
+	const Obj* o;
+};
+
+} // zeek::detail