Add BounaryTag type alias, annotate Mesh.groups

Author: inducer

meshmode/mesh/__init__.py

@@ -22,7 +22,7 @@
 
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, replace, field
-from typing import Any, ClassVar, Hashable, Optional, Tuple, Type
+from typing import Any, ClassVar, Hashable, Optional, Tuple, Type, Sequence
 
 import numpy as np
 import numpy.linalg as la
@@ -66,6 +66,9 @@
 
 # {{{ element tags
 
+BoundaryTag = Hashable
+
+
 class BTAG_NONE:  # noqa: N801
     """A boundary tag representing an empty boundary or volume."""
 
@@ -906,6 +909,8 @@ class Mesh(Record):
     .. automethod:: __ne__
     """
 
+    groups: Sequence[MeshElementGroup]
+
     face_id_dtype = np.int8
 
     def __init__(self, vertices, groups, *, skip_tests=False,