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I've just noticed that the handling of errors in xml:base attributes
is disturbingly unspecified in the XML Base spec, and it's causing me
some problems. For example consider this document which, for the sake
of argument, let us say is loaded from http://www.example.org/:
<root xml:base="http://www.red.com/";>
<child xml:base=" http: //www.green.org/%GG/%z/%8???### ">data</child>
</root>
Although many strings are syntactically correct URIs (especially
given that xml:base allows non-ASCII characters, which are escaped
calculating the URI) I hope it's obvious that there are well-formed
values of xml:base which are not legal URIs, such as in the child
element above.
What is the base URI of the child element? According to the XML Base
spec, the base URI of an element is "the base URI specified by an
xml:base attribute on the element, if one exists". However, in this
case (and many others) the xml:base attribute exists but it does not
provide a URI.
Possibly the problem is grammar, Does the "one" in "if one exists"
refer to the URI, not the xml:base attribute? If so the base URI of
child is http://www.red.com/. But you could also argue that it has no
base URI, or that the base URI is http://www.example.org/. I suspect
implementations vary.
Does anyone know what the intent was in this case, if indeed there
was intent at all? It's possible the working group did not consider
this possibility. However, this is resolved, I think an erratum is
needed to clarify the proper handling of non-URIs that occur in
xml:base attributes.
--
Elliotte Rusty Harold
elharo@metalab.unc.edu
Effective XML (Addison-Wesley, 2003)
http://www.cafeconleche.org/books/effectivexml
http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA
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