I want to be able to display the tsu (ツ) character from Katakana instead of smiley faces on my website.
I already found the byte sequence, which is \343\203\204, but I don't know how to represent this as a XML entity, so that I can display it in a HTML page.
If your XML-to-HTML-transformation stack (and the web server delivering the HTML pages) supports unicode properly, it should be as simple as writing the unicode code point as an entity (&x30c4;). If they don't ... well, good luck ツ
You can always use the character reference ツ (based on the Unicode number in hexadecimal), independently of document encoding.
By notation \343\203\204 you probably mean the octal presentation of three bytes, which constitute the UTF-8 encoded representation of the character. The data consisting of those bytes can be included as such into the XML document, if its encoding is UTF-8 (the default). How you do that depends on the program used to create the XML file.
These considerations also apply to HTML, whether in XHTML format or not. In practice, if you intend to use the character on a web page, there can be font problems, because most fonts do not contain it. Making a suitable font suggestion in CSS is thus a good idea. More info: http://www.cs.tut.fi/~jkorpela/html/characters.html
