add `id` as special-case option in regex. closes #406

stix2/properties.py

@@ -537,7 +537,7 @@ def enumerate_types(types, spec_version):
     return return_types
 
 
-SELECTOR_REGEX = re.compile(r"^[a-z0-9_-]{3,250}(\.(\[\d+\]|[a-z0-9_-]{1,250}))*$")
+SELECTOR_REGEX = re.compile(r"^([a-z0-9_-]{3,250}(\.(\[\d+\]|[a-z0-9_-]{1,250}))*|id)$")
 
 
 class SelectorProperty(Property):

stix2/test/v20/test_granular_markings.py

@@ -1089,3 +1089,17 @@ def test_clear_marking_not_present(data):
     """Test clearing markings for a selector that has no associated markings."""
     with pytest.raises(MarkingNotFoundError):
         data = markings.clear_markings(data, ["labels"])
+
+
+def test_set_marking_on_id_property():
+    malware = Malware(
+        granular_markings=[
+            {
+                "selectors": ["id"],
+                "marking_ref": MARKING_IDS[0],
+            },
+        ],
+        **MALWARE_KWARGS
+    )
+
+    assert "id" in malware["granular_markings"][0]["selectors"]

stix2/test/v21/test_granular_markings.py

@@ -1307,3 +1307,17 @@ def test_clear_marking_not_present(data):
     """Test clearing markings for a selector that has no associated markings."""
     with pytest.raises(MarkingNotFoundError):
         markings.clear_markings(data, ["malware_types"])
+
+
+def test_set_marking_on_id_property():
+    malware = Malware(
+        granular_markings=[
+            {
+                "selectors": ["id"],
+                "marking_ref": MARKING_IDS[0],
+            },
+        ],
+        **MALWARE_KWARGS
+    )
+
+    assert "id" in malware["granular_markings"][0]["selectors"]