combine

[James Clark <jjc@jclark.com>]

> > Getting rid of combine="replace" is pointless unless you get rid of
> > combine="group".  They are both equally order-dependent.  Here's where
my
> > XHTML mod rewrite uses combine="group":
>
> I now believe we can't make RELAX NG an order-insignificant language
> without significant drawback.
>
> But all combine="group"s in XHTML are used to combine attributes. So
> actually they makes no order dependency.

Right.  We could have a restriction on combine="group" that you can't use it
in a way which makes order significant (eg combining two <element>
patterns).  On the other hand that would rule out using combine="group" to
provide functionality similar to derivation of complex types by extension in
XML Schema (adding things on to the end of a content model).

I wonder whether one could attach a priority to definitions to allow
combination without order dependence (like xsl:template).  With
combine="replace", the pattern with the highest priority would be the one
used.  With combine="group", the patterns would be grouped in order of
priority.  You wouldn't be able to mix different kinds of combine for a
single pattern.

James