<internal-file> element and xml:space handling

[Asgeir Frimannsson <asgeirf@redhat.com>]

Hi all,

During our Tuesday teleconference we briefly touched upon the role of 
whitespace in the <internal-file> element. this element does not allow 
attribute extensions, and neither is the 'xml:space' attribute defined for 
this element. 

Someone mentioned that xml-namespace attributes can be added to any element 
and be validated correctly even though they are not defined in the xsd. I had 
the opposite experience, and agreed to investigate this further. 

I used the following sample document:

<?xml version="1.0" encoding="utf-8"?>
<xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" version="1.2">
  <file original="myfile.txt" datatype="plaintext" source-language="en-US">
    <header>
      <skl>
        <internal-file xml:space="preserve"></internal-file>
      </skl>
    </header>
    <body/>
  </file>
</xliff>

I checked this with the libxml2 and xerces-java validators with the result of 
a FAILED validation (Attribute 'xml:space' is not allowed to appear in 
element 'internal-file').

To ensure whitespace is preserved in the internal-file skeleton, xml:space has 
to be set to 'preserve' on the parent <file> element, which is far from 
ideal.

cheers,
asgeir

On Tuesday 19 February 2008 11:53:14 pm Asgeir Frimannsson wrote:
> Hi all,
>
> In XLIFF 1.x whitespace is handled via the standard xml:space attribute,
> and this attribute can be applied to <file>, <group>, <trans-unit> and
> <alt-trans> elements. These elements are all structural containers in that
> they do not allow mixed-content children, only child elements.
>
> file element:
> <xsd:attribute ref="xml:space" use="optional"/>
>
> group element:
> <xsd:attribute default="default" ref="xml:space" use="optional"/>
>
> trans-unit element:
> <xsd:attribute default="default" ref="xml:space" use="optional"/>
>
> alt-trans element:
> <xsd:attribute default="default" ref="xml:space" use="optional"/>
>
> In addition to these, any element that supports attribute extensions
> (namely <alt-trans>, <bin-source>,  <bin-target>,  <bin-unit>, <bpt>, 
> <bx/>, <ept>  , <ex/>,  <file>,  <g>  , <group>,  <it>, <mrk> ,  <ph>,
> <seg-source>,  <source>,  <target>,  <tool>,  <trans-unit>,  <x/>, and
> <xliff>), can also use the 'xml:space' attribute.
>
> Note that a schema-aware XML parser will add any missing default-value
> attributes when parsing a document, causing e.g. the xml:space attribute on
> the <file> element to be somewhat redundant, as this value will be
> overridden on all <group>, <trans-unit> and <alt-trans> elements.
>
> Another example is handling say the <internal-file> element. Here it is
> very important in some cases that whitespace is preserved. However, to
> accomplish this, tools need to set this attribute on the <file> element,
> rather than simply allowing the xml:space attribute on the <internal-file>
> element.
>
> The elements where whitespace handling might be important is the
> content-containers, where the child content is mixed content or text. These
> include  <seg-source>, <target>, <internal-file>, inline elements,
> <context> to name a few.
>
> Let me give an example of another issue with the current whitespace
> handling:
>
> <trans-unit id='1' xml:space='preserve'>
>   <source>hello world!!</source>
> </trans-unit>
>
> Above, I have set the xml:space attribute to 'preserve' to ensure that my
> source text doesn't include any additional whitespace. However, there is a
> problem with this: I do not care about the whitespace e.g. between the
> <trans-unit> opening tag and the <source> opening tag. The above fragment
> could just as well have been written as follows:
>
> <trans-unit id='1' xml:space='preserve'><source>hello
> world!!</source></trans-unit>
>
> However, according to the XML specification, the two fragments above are
> not equal, since the xml:space attribute affects all child elements (unless
> overridden in a child).
>
> I don't have an immediate solution for how we solve these issues for XLIFF
> 2.0, however some initial ideas are:
> 1) Allow attribute-extensions for all mixed-content-elements in the
> specification, or at least all where xml:space would make a difference
> 2) Create a section about Whitespace handling in the specification,
> especially adopting a convention that any <target> element should use the
> same whitespace handling as their sibling <source> element.
> 3) Let XML processors do what they do best, they will honour the xml:space
> attribute :)
>
> cheers,
> asgeir
>
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