XML Max Character Value

I'm implementing B-Tree to index XML documents. I'd like a
    to use maximum character value as a boundry, or failing that a
    minimum character value.

    I'm working in Java.
    
    Is there a maximum character value guarunteed  be greater than
    any other character regardless of the locale? Is that character
    Character.MAX_VALUE?

    Or do I have to read a book on Unicode? Which one?

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Alan Gutierrez - 
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