Re: why the output requirements on viewport?

Would the p:for-each step be a good alternative where you're not going to
connect the output to another port?
-Leif

On Mon, Mar 12, 2012 at 9:13 PM, Conal Tuohy <conal.tuohy@versi.edu.au>wrote:

> **
> Why does the XProc spec require viewports to have a primary output?
> http://www.w3.org/TR/xproc/#err.S0006
>
> The p:viewport must contain a single, *primary output port<http://www.w3.org/TR/xproc/#dt-primary-output-port>
> * declared explicitly or supplied by default<http://www.w3.org/TR/xproc/#primary-input-output>.
> If that port has no *connection<http://www.w3.org/TR/xproc/#dt-connection>
> *, then it is connected to the *primary output port<http://www.w3.org/TR/xproc/#dt-primary-output-port>
> * of the *last step <http://www.w3.org/TR/xproc/#dt-last-step>* in the *
> subpipeline <http://www.w3.org/TR/xproc/#dt-subpipeline>*. It is a *static
> error <http://www.w3.org/TR/xproc/#dt-static-error>* (err:XS0006<http://www.w3.org/TR/xproc/#err.S0006>)
> if the primary output port is unconnected and the *last step<http://www.w3.org/TR/xproc/#dt-last-step>
> * in the subpipeline does not have a primary output port.
>
> http://www.w3.org/TR/xproc/#p.viewport
>
> I can see that it is generally useful to provide an output (when using the
> viewport as a way of transforming a document by transforming chunks of it)
> but equally it's sometimes unnecessary (when using the viewport merely to
> break the document into chunks for independent processing in their own
> right). It seems to me that in those cases where a viewport's sub-pipeline
> merely consumes the sequence of documents without producing any output, the
> viewport could simply remove the matched elements (i.e. it would behave
> like p:delete, seen from the outside).
> --
>
> Conal Tuohy
> eResearch Business Analyst
> Victorian eResearch Strategic Initiative+61-466324297
>
>