Clean the extension listing pages

Author: joshmoore

docs/v3/array-storage-transformers.rst

@@ -2,12 +2,20 @@
 Array Storage Transformers
 ==========================
 
-Under construction.
+.. COMMENT TO BE REMOVED WHEN ONE IS ADDED
 
-.. toctree::
+   The following documents specify transformers which are defined by the maintainers of
+   the Zarr specification. Being listed below does not imply that a transformer is
+   required to be implemented by implementations.
+
+   toctree::
    :glob:
    :maxdepth: 1
    :titlesonly:
    :caption: Contents:
 
    array-storage-transformers/*/*
+
+Currently, no transformers are defined by the maintainers of
+the Zarr specification. Being listed below does not imply that a transformer is
+required to be implemented by implementations.

docs/v3/codecs.rst

@@ -4,7 +4,7 @@ Codecs
 
 The following documents specify codecs which are defined by the maintainers
 of the Zarr specification. Being listed below does not imply that a codec is
-required to be implemented by implementations.
+required to be implemented by all implementations.
 
 .. toctree::
    :glob:

docs/v3/data-types.rst

@@ -2,7 +2,9 @@
 Data Types
 ==========
 
-Under construction.
+The following documents specify data types which are defined by the maintainers of
+the Zarr specification. Being listed below does not imply that a data type is
+required to be implemented by implementations.
 
 .. toctree::
    :glob:

docs/v3/stores.rst

@@ -2,7 +2,8 @@
 Stores
 ======
 
-Under construction.
+The following documents specify stores which are defined by the maintainers of the Zarr specification.
+Being listed below does not imply that a store is required to be implemented by all implementations.
 
 .. toctree::
    :glob:

docs/v3/stores/filesystem/v1.0.rst

@@ -207,4 +207,4 @@ References
 Change log
 ==========
 
-@@TODO
+No changes yet.