XML Demystified

CHAPTER 7 XML Parsers and Transformations
The Error Handler is the component of a SAX parser that responds to errors
discovered by the SAX parser when it’s reading the XML document. There are
three types of errors: warnings, error, and fatal error.
A warning indicates that the SAX parser encountered something unusual in the
XML document, but it wasn’t enough to stop it from transforming the XML
document. An error is more serious than a warning. It doesn’t prevent the parser
from continuing; however, the transformed document might be properly transformed.
A fatal error prevents the SAX parser from continuing.
Each error has a corresponding error handler that’s called when the SAX parser
encounters it. A handler is a method with instructions on how to respond to the
error. These methods are warning(), error(), and fatalError().
You don’t need to be concerned with how error handlers work. However, you do
need to understand how to react to the error messages that these error handlers
display. Each SAX parser has its own set of error messages, so you’ll need to refer
to the documentation that comes with your SAX parser to know how to respond to
error messages.
The DTD Handler
The DTD Handler reads the Data Type Definition (DTD) (see Chapter 3) and then
uses the DTD to validate tags in the XML document. If an XML tag violates the
DTD, the DTD Handler causes the Error Handler to display a warning or error
message on the screen indicating the nature of the problem. We illustrate this in the
following XML document and DTD.
The XML document:
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