private static boolean isComposingChar(int c) {
        return COMPOSING_CHARACTERS.contains(c);
    }
Returns <code>true</code> if the argument is a composing character 
and <code>false</code> otherwise.

@param c a Unicode code point
@return <code>true</code> if the argument is a composing character 
<code>false</code> otherwise
src/nu/validator/checker/NormalizationChecker.java