Character and Entity References
Entity and character references are also often abused. Many XML parser APIs sometimes let you see which entity any given character came from (though not all do, and in SAX and DOM this ability is not implemented by all parsers). However, you shouldn't rely on this, and no parsers will tell you whether each character came from raw text or a character reference.
The classic example of what not to do here is to mix XML's escaping mechanisms with your application's escaping mechanism. For instance, an application could specify that a string of text beginning with a literal dollar sign ($, Unicode character 36) is a variable reference. For example, the following Para element includes a variable reference.
<Para>Hello ...
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