What can we expect (from processors)

Hello XProc friends,

Maybe this is covered in the specs, if so please direct me!

I am needing to know more about what I can expect from an XProc engine.

Briefly, if I bind an input using a port, and then my XProc never uses it,
can I hope it will never be accessed (located and parsed)?

How about documents loaded using p:load?

Examples:

- A static option 'skip' is set to a Boolean
- A document is given on the main input port
- A p:load is given that says 'use-when="$skip"'
- Nowhere does a step bind to the main input

Will the document on the main input port be loaded?

Same question can be asked with p:variable and p:if or p:choose wrappers
(i.e., not use-when).

And lastly, the same question(s) again, only this time all dynamic loading
- will a p:load be loaded if its results are never bound to anything? (say,
another p:load happens.)

Should one generally assume everything is always loaded, if a port binding
is given? Or always loaded, period, even if subsequent steps make no use of
step outputs (or port bindings)?

If all this is processor dependent (and even if not), how could one learn
more? is this the kind of thing that 'trace' options will show?

Lift a pint for me in London! - Wendell

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