Steps with no input/output ports

Hello,

Just wondering: Do we need to say anything special about atomic/compound
steps that are declared as having no input ports and/or no output ports?
For instance, consider the following declaration of an atomic step:

<p:declare-step type="foo:do-some-magic"/>

The fact that the step has no inputs/outputs can have interesting (or
surprising) consequences for the user if he uses it in a pipeline. For
instance, the XProc processor is completely free to decide when to
execute the step since it has no explicit connections to other steps.

My feeling is that these "degenerated" cases are covered sufficiently in
the spec, but perhaps there are cases that we didn't foresee? Has
anybody thought about this?


Regards,
Vojtech