Default binding for variable, option, parameter definitions

At the risk of being taken behind the woodshed and beaten to within an
inch of my life by other members of the WG, since we are going back to
Last Call anyway, I'd like the WG to consider one other change.

Aside from being a pointless way to set the path to "..", at present,
the following pipeline is not valid:

  <p:declare-step>
    <p:output port="result"/>

    <p:directory-list>
      <p:with-option name="path" select="concat('.','.')"/>
    </p:directory-list>
  </p:declare-step>

It's not valid because there's no default readable port and there's
no explicit XPath context established for the evaluation of the select
expression. The most common way to make it valid is thus:

  <p:declare-step>
    <p:output port="result"/>

    <p:directory-list>
      <p:with-option name="path" select="concat('.','.')">
        <p:empty>
      </p:with-option>
    </p:directory-list>
  </p:declare-step>

In writing real-life pipelines, I've actually found this to be a
significantly tedious problem. It seems clear to me that an
alternative interpretation of the former pipeline would be to say that
if there's no default readable port and no explicit binding, that the
context is undefined and references to the context are an error.

I believe the WG discussed this and explicitly chose the current
status quo. I can no longer recall (nor have I been able to find,
though I admit I haven't looked very hard, record of) why we did this.

The only negative consequence I can see to this change is that an
XPath 1.0 implementation has no way of representing an "undefined"
context and so an XPath 1.0 implementation would fail to detect some
errors.

If someone can remind me of some other negative consequence, I'd
appreciate it.

I think, on balance, I would prefer to allow an XPath 1.0
implementation to sometimes give the wrong answer rather than force
every user to insert explicit empty bindings in what turn out in my
experience to be a great many places.

I didn't consider this a significant enough irritation to warrant
going back to Last Call to fix it, but if we have to go back to Last
Call anyway, I propose that we change the rules so that if there's no
default readable port and no explicit binding, the context is
undefined and references to the context are an error.

I think the users will thank us.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | I have animal magnetism. When I go
http://nwalsh.com/            | outside, squirrels stick to my clothes.