What does NSXMLParserUndeclaredEntityError mean?

When using NSXMLParser, what does NSXMLParserUndeclaredEnti开发者_StackOverflow社区tyError mean? Apples documentation is completely unhelpful

Have a look at the first answer on Resolving html entities with NSXMLParser on iPhone where it lists the standard supported entities. Are you able to post your XML that you're parsing?

You get the NSXMLParserUndeclaredEntityError when you use a special character that isn't expected by the NSXMLParser for example &foo;

The only valid special characters that the NSXMLParser will recognize are:

<
>
'
"