[_707,_768] README sections

Author: d-w-moore

README.md

@@ -832,6 +832,67 @@ of create and modify timestamps for every AVU returned from the server:
 datetime.datetime(2022, 9, 19, 15, 26, 7)
 ```
 
+Disabling AVU reloads from the iRODS server
+-------------------------------------------
+
+With the default setting of reload = True, an iRODSMetaCollection will
+proactively read all current AVUs back from the iRODS server after any
+metadata write done by the client.  This helps methods such as items()
+to return an up-to-date result.   Changing that default can, however, greatly
+increase code efficiency if for example a lot of AVUs must be added or deleted
+at once without reading any back again.
+
+```
+# Make a metadata view in which AVUs are not reloaded, for quick update:
+non_current_metadata_view = obj.metadata(reload = False)
+for i in range(10):
+    non_current_metadata_view.add("my_key", "my_value_"+str(i))
+
+# Force reload of AVUs and display:
+current_metadata = obj.metadata().items()
+from pprint import pp
+print(f"{current_metadata = }")
+```
+
+Subclassing iRODSMeta
+---------------------
+The keyword option `iRODSMeta_type` can be used to set up any iRODSMeta
+subclass as the translator between native iRODS metadata APIs
+and the way in which the AVUs thus conveyed should be represented to the
+client.
+
+An example is the `irods.meta.iRODSBinOrStringMeta` class which uses the
+`base64` module to "hide" arbitrary bytestrings within the `value` and
+`units` attributes of an iRODS metadata AVU:
+
+```
+from irods.meta import iRODSBinOrStringMeta as MyMeta
+d = session.data_objects.get('/path/to/object')
+unencodable_octets = '\u1000'.encode('utf8')[:-1]
+
+# Use our custom client-metadata type to store arbitrary octet strings
+meta_view = d.metadata(iRODSMeta_type = MyMeta)
+meta_view.set(m1 := MyMeta('mybinary', unencodable_octets, b'\x02'))
+
+# Show that traditional AVU's can exist alongside the custom kind.
+irods.client_configuration.connections.xml_parser_default = 'QUASI_XML'
+meta_view.set(m2 := MyMeta('mytext', '\1', '\2'))
+
+try:
+    # These two lines are equivalent:
+    assert {m1,m2} <= (all_avus := set(meta_view.items()))
+    assert {tuple(m1),tuple(m2)} <= all_avus
+finally:
+    del meta_view['mytext'], meta_view['mybinary']
+```
+
+Whereas the content of native iRODS AVUs must obey some valid text encoding as
+determined by the resident ICAT DB, the above is a possible alternative - albeit
+one semantically bound to the local application that defines the needed
+translations.  Still, this can be a valid usage for users who need a guarantee
+that any given octet string they might generate can be placed into metadata without
+violating standard text encodings.
+
 Atomic operations on metadata
 -----------------------------