Re: SVGt 1.2: processing invalid external URI references

>A halfway house is to have something like HTML object that allows the 
>author to provide explicit fallback rules (it may exist already - 
>switch???).

switch in SVGT1.2 with the attribute requiredFormats can do
similar things as (X)HTML object with type.
If an external resource is not available
externalResourcesRequired may help authors to cover a
situation with a(nother) server having currently a 
problem, the runtime synchronization attributes may help, 
if the other server is just a little bit lazy, but still able to answer
requests.
But there is no specific attribute to cover typos of the
author in the xlink:href attribute to switch to an alternative IRI
without a typo ;o)