SAX: ModSAX addition, general property query

[Glenn Vanderburg]

Bill la Forge wrote:
> 
> From: John Wilson <tug at wilson.co.uk>
> >I don't think that it's unreasonable to insist that objects 
> >representing a Feature, Handler or Property should either implement 
> >a distinct interface or subclass a distinct class. If this is so 
> >the Parser can tell what Feature, Handler or Property is being set 
> >by enquiring of the type of the object.
> 
> Filters often implement more than one (generally all) handler 
> interface and then register themselves with the underlying 
> parser/filter for the same events requested by the overlaying 
> application/filter.

Yes, and as written, John's proposal would require distinct handler
objects for each feature, which would be bad.  However, with a slight 
modification, it would work beautifully.  Instead of using a string 
as a feature ID, use a type descriptor (in Java, an instance of 
java.lang.Class).  Feature handlers would be registered by supplying 
the Class object that represents the feature being implemented, along 
with a handler object that is assignable to that type.

It seems probable to me that, whatever naming scheme is chosen for 
features, each feature will have a special interface that handlers 
must implement; if that's true, and Strings are used to identify 
features, we will effectively have two names for each feature.  And 
using classes shares one of the good aspects of the URI solution: it 
piggybacks on the DNS to provide a ready-made collision-free global 
namespace.

The only problem I see with this proposal is that it may not translate
well to other languages.  One possibility is for other languages to use
the name of the corresponding Java interface as a feature name; for
example, "org.xml.sax.NamespaceHandler".  This may not be ideal, but
does not seem too onerous.

---glv

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