RE: [xml-dev] Why do W3C specifications have "implementation defined" pa

["Michael Kay" <mike@saxonica.com>]

1. xsl:message is a classic example of a language feature that interacts
with the external environment in which the XSLT processor operates. Because
XSLT processors may operate in many different environments, it's not
possible to mandate the effect the instruction has on any particular
environment. 

There may be cases where (as David Carlisle suggests) things have been left
implementation-defined simply because implementors on the working group
could not come to agreement. This isn't one of them. Even in those cases
there may be a reasonable justification based on the cost of implementation,
or the effort involved in specifying the behaviour. Standardisation of
collation URIs comes to mind.

2. Yes, many other specifications have similar provisions. The terms
"implementation-defined" and "implementation-dependent" come from the SQL
world.

Michael Kay


> 
> In many of the W3C specifications there are parts that are 
> "implementation defined."
> 
> To give one example, in the XSLT specification it says this 
> about the <xsl:message> element [1]:
> 
>     The xsl:message instruction sends a message in an 
> implementation-defined way. 
>     The xsl:message instruction causes the creation of a new 
> document, which is 
>     typically serialized and output to an 
> implementation-defined destination.
> 
> 
> QUESTIONS:
> 
> 1. The purpose of a specification is to define a standard. 
> Doesn't "implementation defined" defeat that purpose since it 
> means that each vendor will define their implementation in 
> their own way, thereby obviating standardization?
> 
> 2.Is this unique to the W3C? Do other standards organizations 
> also have "implementation defined" sections in their specifications?
> 
> 
> /Roger
> 
> [1] http://www.w3.org/TR/2007/REC-xslt20-20070123/#message 
> 
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