be stated in the query string for a URL.   Custom plugins can
be written which will be given the chance up front to alter and/or
consume the engine's URL and keyword arguments, and then at engine
create time will be given the engine itself to allow additional
modifications or event registration.  Plugins are written as a
subclass of :class:`.CreateEnginePlugin`; see that class for
details.
fixes #3536

:func:`.engine_from_config` were not being parsed correctly;
these included ``pool_threadlocal`` and the psycopg2 argument
``use_native_unicode``. fixes #3435
- add legacy_schema_aliasing config parsing for mssql
- move use_native_unicode config arg to the psycopg2 dialect

functionality.   Added a new "soft invalidate" feature to the
connection pool at the level of the checked out connection wrapper
as well as the :class:`._ConnectionRecord`.  This works similarly
to a modern pool invalidation in that connections aren't actively
closed, but are recycled only on next checkout; this is essentially
a per-connection version of that feature.  A new event
:class:`.PoolEvents.soft_invalidate` is added to complement it.
fixes #3379

- Added new flag
:attr:`.ExceptionContext.invalidate_pool_on_disconnect`.
Allows an error handler within :meth:`.ConnectionEvents.handle_error`
to maintain a "disconnect" condition, but to handle calling invalidate
on individual connections in a specific manner within the event.

- Added new event :class:`.DialectEvents.do_connect`, which allows
interception / replacement of when the :meth:`.Dialect.connect`
hook is called to create a DBAPI connection.  Also added
dialect plugin hooks :meth:`.Dialect.get_dialect_cls` and
:meth:`.Dialect.engine_created` which allow external plugins to
add events to existing dialects using entry points.
fixes #3355

:paramref:`.Pool.reset_on_return` parameter as a synonym for ``None``,
so that string values can be used for all settings, allowing
.ini file utilities like :func:`.engine_from_config` to be usable
without issue.
fixes #3375

they don't really belong into a new suite in test_execute

differently for the case where it is called in an already-invalidated state;
don't call upon self.connection

to it, so that we say we will do the wrapping just once right here
in _execute_context() / _execute_default().  An adjustment is made
to _handle_dbapi_error() to not assume self.__connection in case
we are already in an invalidated state

further adjustment to
0639c199a547343d62134d2f233225fd2862ec45, 41e7253dee168b8c26c49, #3266

_handle_dbapi_error(); these are now handled already and the reentrant
call is not needed / breaks things.  Adjustment to 41e7253dee168b8c26c49 /

take effect in all engine connection use cases, including
when user-custom connect routines are used via the
:paramref:`.create_engine.creator` parameter, as well as when
the :class:`.Connection` encounters a connection error on
revalidation.
fixes #3266