@Override
    public final boolean sameValue(Object value1, Object value2) {
        if (value1 == null) {
            return (value2 == null);
        }
        return value1.equals(value2);
    }
Implements strict string equality semantics by performing a standard 
<code>equals</code> check on the arguments.
@param value1 an object returned by <code>createValue</code>
@param value2 another object returned by <code>createValue</code>
@return <code>true</code> if the values are equal, <code>false</code> otherwise
@see org.relaxng.datatype.Datatype#sameValue(java.lang.Object, java.lang.Object)
src/nu/validator/datatype/AbstractDatatype.java