viewport

taking the definition of a sub pipeline

http://www.w3.org/XML/XProc/docs/langspec.html#dt-subpipeline

and the definition of viewport

how can the spec example be correct

4.3.2 Example

or rephrased;

    Is a viewport naturally a subpipeline?

or

    Is it envisaged that the subpipeline, within a viewport, should
encapsulated.... e.g. should there be a

(p:for-each|p:viewport|p:choose|p:group|p:try|pfx:other-step|p:documentation|ipfx:ignored)*

element? taking the 4.3.2 example

<p:viewport match="h:div[@class='chapter']"
            xmlns:h="http://www.w3.org/1999/xhtml">
<p:group>
  <p:insert at-start="true">
    <p:input port="insertion">
      <p:inline>
        <hr xmlns="http://www.w3.org/1999/xhtml"/>
      </p:inline>
    </p:input>
  </p:insert>
</p:group>
</p:viewport>

is there any default encapsulation if this wrapping element is omitted?

another related question with viewport and I guess generally about
subpipelines is if there is a need to provide some more 'words' on
error handling ?

cheers, JIm Fuller