I was under the impression that the "default default collation" (for XPath eq comparison, etc) was defined to be Unicode codepoint collation. But reading the spec, it says that for the use-when attribute, but it doesn't seem to say it for anything else. Section 5.4.1 points to 3.6.1:

The default collationXP is defined by the value of the [xsl:]default-collation attribute on the innermost enclosing element that has such an attribute. For details, see 3.6.1 The default-collation attribute.

but neither this nor 3.6.1 says what the rules are in the absence of such an attribute.

We ought either to say that the "default default" is the Unicode codepoint collation, or that it is implementation-defined. My preference is for the former (which I had always imagined was what the spec said).

This arose from a question on xsl-list today from Vyacheslav Sedov discussing whether it was legitimate to perform Unicode normalization as part of an "eq" comparison.