API, used for any expression construct that can be sent to
execute(). FunctionElement now inherits Executable so that
it gains execution_options(), which are also propagated
to the select() that's generated within execute().
Executable in turn subclasses _Generative which marks
any ClauseElement that supports the @_generative
decorator - these may also become "public" for the benefit
of the compiler extension at some point.
same way any func.foo() construct is, with automatic
SELECT being applied when passed to execute().
- The "type" and "bind" keyword arguments of a func.foo()
construct are now local to "func." constructs and are
not part of the FunctionElement base class, allowing
a "type" to be handled in a custom constructor or
class-level variable.
Mike Bayer