Scope of xml:base

In http://www.w3.org/TR/2000/WD-xmlbase-20000221#AEN1_4_2_2

1)
"The base URI specified by xml:base sets the base URI information set property
of the element on which this attribute occurs, .."

and

2)
"The value of the xml:base attribute may itself be a relative URI, in which
case it must itself be resolved against the base URI of the element it appears
on."

The document http://www.example.com contains :

<c xml:base="x/">
  <b xml:base="y/">
    <a href="z/doc.xml>activate here</a>
    <d xml:base='http://www.example.com/slurp.xml'/>
  </b>
</c>

According to 1), the base URI information set properties are :

[document]  http://www.example.com
c           http://www.example.com/x
b           http://www.example.com/x/y
a           http://www.example.com/x/y
d           http://www.example.com/slurp.xml
a/@href     doesn't have a base URI property
a/text()    don't have a base URI property

Absolute URI of href is :
a           http://www.example.com/x/y/z/doc.xml

According to 2), the base URI of b is used to resolve the absolute
URI of his attribute xml:base which is supposed to specify the base URI
of the element b !?!?

Philippe.