Following-or-end in xslt/xpath?

XPath Axes contain the directive following:: to obtain the set of all following nodes.

Given for instance the following file:

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <a/>
    <b/> <!-- access 1 -->
    <a/>
    <ca/>
    <a/>
    <b/>
    <a/>
    <a/>
    <cb/>
    <b/> <!-- access 2 -->
</foo>

One can for instance use following::a/preceding::b[1] to access access 1 given <ca>. In other words one wish to access:

the "last" <b> before the next <a>.

If the current node is however <cb>, that trick doesn't work anymore, since there is no following::a. Is there a following-or-end directive (or something equivalent) that in that case returns the last tag (</foo>), such that access 2 can be obtained from <cb/>?

Such following-or-next should be read as:

The next <a> or the end of the file in case this doesn't exist.