XML in a Nutshell, 3rd Edition

References

The character data inside an element must not contain a raw unescaped opening angle bracket (<). This character is always interpreted as beginning a tag. If you need to use this character in your text, you can escape it using the entity reference < , the numeric character reference <, or the hexadecimal numeric character reference <. When a parser reads the document, it replaces any <, `, or < references it finds with the actual < character. However, it will not confuse the references with the starts of tags. For example:

<SCRIPT LANGUAGE="JavaScript">
  if (location.host.toLowerCase( ).indexOf("ibiblio") &lt; 0) {
    location.href="http://ibiblio.org/xml/";
  }
</SCRIPT>

Character data may not contain a raw unescaped ampersand (&) either. This is always interpreted as beginning an entity reference. However, the ampersand may be escaped using the & entity reference like this:

<company>W.L. Gore &amp; Associates</company>

The ampersand is code point 38 so it could also be written with the numeric character reference &:

<company>W.L. Gore &#38; Associates</company>

Entity references such as & and character references such as < are markup. When an application parses an XML document, it replaces this particular markup with the actual character or characters the reference refers to.

XML predefines exactly five entity references. These are:

<

The less-than sign, a.k.a. the opening angle bracket (<)

&

The ampersand (&)

>

The greater-than sign, ...