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Custom functions (Major re-write, please review)

From: Nick Van den Bleeken <Nick.Van.den.Bleeken@inventivegroup.com>
Date: Thu, 8 Mar 2012 17:22:14 +0000
To: Public Forms <public-forms@w3.org>
Message-ID: <141DF291-5DDB-4691-AF23-4AE065EDECC5@inventivegroup.com>

I've updated http://www.w3.org/MarkUp/Forms/wiki/Custom_XPath_functions I tried to make the text more XForms spec like (no longer XSLT spec like)

I made one change to what we agreed on the call yesterday.

The current spec doesn't allows you to intermix script and sequence child elements. I did this because you are allowed to use multiple sequence (and script) elements as the body of a function element to allow easy creation of result sequences. And if you allow multiple sequence (and script) elements it becomes a bit unclear what you want to achieve when you intermix those.

But I allow the author to override already defined functions. I also added an extra attribute override to let the author choose if he wants to override already defined functions. This has the nice consequence that a form author could use XForms implementation specific functions but include a declaration of those functions that will be used in implementations that don't have those functions (by setting override to no).

I put an example of how to fall back to an XPath implementation of a function if the processor doesn't support javascript in 'specification'.

If the form author writes the example like this it would even default to the native implementation if the XForms implementation has implemented the function:

<function name="my:foo" as="number" override="no">
   <param name="p" as="nodeset"/>

   <script type="text/javascript">

<function name="my:foo" as="number" override="no">
   <param name="p" as="nodeset"/>

   <sequence select="sum($p)"/>

As you can see in the example I name spaced all 'variables' this is best practice in javascript and many other languages.


I also needed to delete the following example because 'Within the body of a custom function, the focus is initially undefined; this means that any attempt to reference the context item, context position, or context size is a non-recoverable dynamic error.' I would like to follow XSLT's take on this, because this allows you to 'import' the function from anywhere without unexpected side effects.

Example: function selecting all elements called "name" in an instance.

<function name="my:get-names" as="nodeset">
    <sequence select="//name"/>

All comments are very welcome.

Kind regards,

Nick Van den Bleeken
R&D Manager

Phone: +32 3 425 41 02
Office fax: +32 3 821 01 71



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Received on Thursday, 8 March 2012 17:22:43 UTC

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