remove leading - from type name re

stix2/core.py

@@ -10,7 +10,7 @@ import stix2
 from .base import _Observable, _STIXBase
 from .exceptions import ParseError
 from .markings import _MarkingsMixin
-from .utils import PREFIX_21_REGEX, TYPE_21_REGEX, TYPE_REGEX, _get_dict
+from .utils import PREFIX_21_REGEX, TYPE_21_REGEX, TYPE_REGEX, EXT_21_REGEX, _get_dict
 
 STIX2_OBJ_MAPS = {}
 
@@ -319,7 +319,7 @@ def _register_observable_extension(
                 ext_type,
             )
     else:  # 2.1+
-        if not re.match(TYPE_21_REGEX, ext_type):
+        if not re.match(EXT_21_REGEX, ext_type):
             raise ValueError(
                 "Invalid extension type name '%s': must only contain the "
                 "characters a-z (lowercase ASCII), 0-9, hyphen (-), "

stix2/test/v21/test_custom.py

@@ -58,6 +58,19 @@ def test_identity_custom_property():
         )
     assert "must begin with an alpha character." in str(excinfo.value)
 
+    with pytest.raises(stix2.exceptions.InvalidValueError) as excinfo:
+        stix2.v21.Identity(
+            id=IDENTITY_ID,
+            created="2015-12-21T19:59:11Z",
+            modified="2015-12-21T19:59:11Z",
+            name="John Smith",
+            identity_class="individual",
+            custom_properties={
+                "_foo": "bar",
+            },
+        )
+    assert "must begin with an alpha character." in str(excinfo.value)
+
     identity = stix2.v21.Identity(
         id=IDENTITY_ID,
         created="2015-12-21T19:59:11Z",

stix2/utils.py

@@ -27,8 +27,8 @@ NOW = object()
 STIX_UNMOD_PROPERTIES = ['created', 'created_by_ref', 'id', 'type']
 
 TYPE_REGEX = re.compile(r'^\-?[a-z0-9]+(-[a-z0-9]+)*\-?$')
-TYPE_21_REGEX = re.compile(r'^\-?([a-z][a-z0-9]*)+(-[a-z0-9]+)*\-?$')
-EXT_21_REGEX = re.compile(r'^\-?([a-z][a-z0-9]*)+(-[a-z0-9]+)*\-ext$')
+TYPE_21_REGEX = re.compile(r'([a-z][a-z0-9]*)+(-[a-z0-9]+)*\-?$')
+EXT_21_REGEX = re.compile(r'([a-z][a-z0-9]*)+(-[a-z0-9]+)*\-ext$')
 PREFIX_21_REGEX = re.compile(r'^[a-z].*')