With tcl build with the defaults as shipped, one isn't able to process all data, which can transported with XML. Because of the charatery entity mechanism of XML, even characters beyond BMP can be expressed in 7-bit ASCII. (If you're not so sure, what this XML speech is all about but you're on top with tcl, think about it as \Uhhhhhh.) tDOM will disgest all Unicode character and will it give back serialized (characters beyond BML as characters entites).