ArraySpec docs

fix documentation to be more accurate around nonspatial arrays

gunpowder/array_spec.py

@@ -14,13 +14,12 @@ class ArraySpec(Freezable):
         roi (:class:`Roi`):
 
             The region of interested represented by this array spec. Can be
-            ``None`` for :class:`BatchProviders<BatchProvider>` that allow
-            requests for arrays everywhere, but will always be set for array
-            specs that are part of a :class:`Array`.
+            ``None`` for nonspatial arrays but must otherwise always be set.
 
         voxel_size (:class:`Coordinate`):
 
-            The size of the spatial axises in world units.
+            The size of the spatial axises in world units. Can be ``None`` for
+            nonspatial arrays but must otherwise always be set.
 
         interpolatable (``bool``):
 
@@ -55,7 +54,10 @@ def __init__(
 
         if nonspatial:
             assert roi is None, "Non-spatial arrays can not have a ROI"
-            assert voxel_size is None, "Non-spatial arrays can not " "have a voxel size"
+            assert voxel_size is None, "Non-spatial arrays can not have a voxel size"
+        else:
+            assert roi is not None, "Spatial arrays must have a ROI"
+            assert voxel_size is not None, "Spatial arrays must have a voxel size"
 
         self.freeze()