Use the xml:lang attribute to set the collation?

Hi Folks,

Michael Kay wrote this response to a StackOverflow question [1]:

    Saxon's default collation is Unicode codepoint, which is fast
    but not smart. Setting lang="en" will immediately give you a
    smarter natural-language collation. There are then many
    options to refine it further.

QUESTIONS
1. Does Michael's response mean that, to set the collation, I can use the
xml:lang attribute instead of the default-collation attribute?

2. Would you please give an example of a comparison where the result of the
comparison is true when xml:lang="A" but false when xml:lang="B"? That is,
what values would you place in here:

    <Test xml:lang="__">
        <xsl:value-of select=" '__' lt '__' " />
    </Test>

/Roger

[1]
http://stackoverflow.com/questions/13052896/xslt-sort-edge-case-for-ascending
-sort-by-element-name