The creators of the XML specification were well aware that different documents may need different character encodings. So they let you specify the encoding right at the top of each document in the XML declaration:

<?xml  version="1.0"  encoding="iso-8859-1"?>

In this example, the encoding is specified as iso-8859-1 which is also known as ISO Latin 1. If the encoding is not specified, then UTF-8 encoding is assumed. With the encoding established, an XML program that opens the document knows how to convert the numbers it sees to logical characters, and then convert those characters into the Unicode numbers it uses internally. Of course, the content of the document must actually be encoded with this encoding. That is, you can't just change the label at the top and think you have a new encoding. The document itself would have to be converted to the new mapping of characters. If the encoding declaration of the document does not match the actual encoding, then you may end up with gibberish.

Here are several common encoding names. Usually either uppercase or lowercase letters are recognized. But don't forget the hyphens.

What if you need to enter a character that a document's encoding does not include? For example, iso-8859-1 does not include a character for the trademark symbol ™. The solution is to use numerical character entities for any characters not in your encoding. The trademark symbol can be entered as ™ in hexadecimal notation, or the equivalent ™ in decimal notation. Of course, having to remember that ™ means trademark is an author's nightmare. Fortunately, the DocBook DTD provides more easily recognized text entities for hundreds of characters you might need. The following is one example from the DTD, this one declared in the iso-num.ent entities file.

<!ENTITY trade      "&#x2122;"> <!-- TRADE MARK SIGN -->

So you just need to enter ™ in your document, and the DTD converts that to the numerical Unicode character that all XML applications recognize. You can examine the complete set of available character entities by looking in the directory that contains the DocBook DTD. The ent subdirectory contains a number of iso-something.ent files, where something identifies the set of entity declarations in that file.

It is entirely possible to write a document in any language that is supported by Unicode using only ASCII characters. All characters beyond the basic ASCII character set are written using numerical character references such ÿ for á, and so on. If you want to see examples of such XML files, look at the files containing generated text strings, such as fr.xml in the common directory of the DocBook XSL distribution. Those files for all languages are encoded as ASCII XML files using numerical character references. The raw XML isn't very readable, however, unless it is displayed in a program that converts such numerical Unicode references to displayable glyphs.