Documented internals used by datasette-hashed-urls

Closes #1663

docs/internals.rst

@@ -217,12 +217,18 @@ You can create your own instance of this - for example to help write tests for a
         }
     })
 
+Constructor parameters include:
+
+- ``files=[...]`` - a list of database files to open
+- ``immutables=[...]`` - a list of database files to open in immutable mode
+- ``metadata={...}`` - a dictionary of :ref:`metadata`
+
 .. _datasette_databases:
 
 .databases
 ----------
 
-Property exposing an ordered dictionary of databases currently connected to Datasette.
+Property exposing a ``collections.OrderedDict`` of databases currently connected to Datasette.
 
 The dictionary keys are the name of the database that is used in the URL - e.g. ``/fixtures`` would have a key of ``"fixtures"``. The values are :ref:`internals_database` instances.
 
@@ -582,6 +588,13 @@ The arguments are as follows:
 
 The first argument is the ``datasette`` instance you are attaching to, the second is a ``path=``, then ``is_mutable`` and ``is_memory`` are both optional arguments.
 
+.. _database_hash:
+
+db.hash
+-------
+
+If the database was opened in immutable mode, this property returns the 64 character SHA-256 hash of the database contents as a string. Otherwise it returns ``None``.
+
 .. _database_execute:
 
 await db.execute(sql, ...)