levels; :meth:`.Connection.get_isolation_level`,
:attr:`.Connection.default_isolation_level`.
- enhance documentation inter-linkage between new accessors,
existing isolation_level parameters, as well as in
the dialect-level methods which should be fully covered
by Engine/Connection level APIs now.

now be constructed such that the visit methods receive an indication
of the owning expression object, if any.  Any visit method that
accepts keyword arguments (e.g. ``**kw``) will in most cases
receive a keyword argument ``type_expression``, referring to the
expression object that the type is contained within.  For columns
in DDL, the dialect's compiler class may need to alter its
``get_column_specification()`` method to support this as well.
The ``UserDefinedType.get_col_spec()`` method will also receive
``type_expression`` if it provides ``**kw`` in its argument
signature.
fixes #3074

sort_tables_and_constraints function.
- The DDL generation system of :meth:`.MetaData.create_all`
and :meth:`.Metadata.drop_all` has been enhanced to in most
cases automatically handle the case of mutually dependent
foreign key constraints; the need for the
:paramref:`.ForeignKeyConstraint.use_alter` flag is greatly
reduced.  The system also works for constraints which aren't given
a name up front; only in the case of DROP is a name required for
at least one of the constraints involved in the cycle.
fixes #3282

and extensions into an external library, and also reorganizes most large documentation
pages into many small areas to reduce scrolling and better present the context
into a more fine-grained hierarchy.

and regexp parsing of SQL in order to form a complete picture of
constraints + their names.  fixes #3244 fixes #3261
- factor various PRAGMA work to be centralized into one call

:class:`.sqlite.TIME`,
or :class:`.sqlite.DATETIME` types, and given a ``storage_format`` that
only renders numbers, will render the types in DDL as
``DATE_CHAR``, ``TIME_CHAR``, and ``DATETIME_CHAR``, so that despite the
lack of alpha characters in the values, the column will still
deliver the "text affinity".  Normally this is not needed, as the
textual values within the default storage formats already
imply text.
fixes #3257

collection has been made consistent; this attribute is now a
:class:`.ColumnCollection` like that of all other constraints and
is initialized at the point when the constraint is associated with
a :class:`.Table`.
fixes #3243

requests for it soon.

test both memory and file-based
- When selecting from a UNION using an attached database file,
the pysqlite driver reports column names in cursor.description
as 'dbname.tablename.colname', instead of 'tablename.colname' as
it normally does for a UNION (note that it's supposed to just be
'colname' for both, but we work around it).  The column translation
logic here has been adjusted to retrieve the rightmost token, rather
than the second token, so it works in both cases.   Workaround
courtesy Tony Roberts.
fixes #3211