I'm a little (ok a LOT) confused between the difference of 'contained steps' and
'subpipeline'

E.g in the spec in this part: 4.1

<p:pipeline name? = NCName type? = QName psvi-required? = boolean xpath-version? = string exclude-inline-prefixes? = prefix list> (p:input | p:output | p:option | p:log | p:serialization)*, (p:declare-step | p:import)*, subpipeline </p:pipeline>

What's the difference between the sequence of p:declare-step and subpipeline ? What really confuses me is this comment : from 2.1

------ Note User-defined pipelines (identified with pfx:user-pipeline in the preceding
syntax summary) are atomic. A pipeline declaration may contain a subpipeline,
but the invocation of that pipeline does not.

------

So that last sentance ... is it saying the "subpipeline" in the above p:pipeline
is not executed ?

If so what is done with it ?

Any references to examples would be greatly appreciated.

Thank you !

-David Lee