value of required extension in conditional processing

Hi
 
I am in the process of developing an SVGTiny player. It works pretty much fine at this point, however, I am having little problem in understanding conditional processing.
 
In SVG conditional processing  ( http://www.w3.org/TR/SVG11/struct.html#ConditionalProcessing ) there is "required extention" attribute. According to spec, the value of "required extension" identified by URL reference ( http://www.w3.org/TR/SVG11/struct.html#URIReference ). It is not easily understandable, what are the possible values? From the spec "The URI names for the extension should include versioning information, such as "http://example.org/SVGExtensionXYZ/1.0", so that script writers can distinguish between different versions of a given extension." 
 
What kind of SVG extension we are talking about? Does this mean that, if the user agent (in this case our SVGTiny player) supports any of the extension it would be statically(compile time information) known to the player?  Can you give me one or two examples? Even after several days of searching I could not find any example on net.

thanks

ruben

 




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