core codecs: MUST support -> SHOULD support

Author: d-v-b

docs/v3/codecs.rst

@@ -5,11 +5,7 @@ Codecs
 Core codecs
 -----------
 
-The following documents specify the codecs that Zarr version 3 implementations MUST support. This collection of 
-codecs is chosen to form a shared basis for interoperability between Zarr implementations in different languages,
-and to ensure that different Zarr implementations consistently implement key Zarr features.
-
-Read more about core codecs in the :ref:`core codecs <core-codecs>` section of the Zarr version 3 specification.
+The following documents specify the core codecs. Read more about core codecs in the :ref:`core codecs <core-codecs>` section of the Zarr version 3 specification.
 
 .. toctree::
    :glob:

docs/v3/core/v3.0.rst

@@ -1220,8 +1220,8 @@ Specifying codecs
 Core codecs
 -----------
 
-This spec defines a set of codecs ("core codecs") which all Zarr implementations MUST implement. 
-This requirement is intended to ensure a minimal level of interoperability between Zarr implementations.
+This spec defines a set of codecs ("core codecs") which all Zarr implementations SHOULD implement in 
+order to ensure a minimal level of interoperability between Zarr implementations.
 Core codecs are each defined by specification documents which are hosted in the
 `zarr-specs GitHub repository`_, and are published on the `zarr-specs documentation web site
 <https://zarr-specs.readthedocs.io/>`_. The list of core codecs is part of the Zarr v3 specification.