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Tatsuhiko Miyagawa > XML-Liberal > XML::Liberal::Error



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This information is for people hacking on XML::Liberal; it's not public API documentation.

There are three sorts of class that cooperate to do the liberal parsing: the error class, a driver, and a remedy class.

Instances of the error class, XML::Liberal::Error, encapsulate the details of an error detected by an XML parser. They have fields message, line, column, and location extracted from a parser error; location is the position within the string of the location described by the error. They also have a method summary, which combines those pieces of information in a human-readable way).

A driver knows how to extract line/column/location/message from exceptions generated by a particular XML parser. It is a subclass of XML::Liberal; the only current driver is XML::Liberal::LibXML, which handles parser exceptions thrown by XML::LibXML. The driver subclass must implement a method extract_error, which takes an exception argument and a reference to the XML source text, and returns a suitable instance of XML::Liberal::Error.

Each remedy has a class method apply which takes three arguments, a driver instance, an error instance, and a reference to the XML source text. It either (a) does nothing and returns false (to indicate that it doesn't know how to fix this problem, so other remedies should be given the opportunity to do so); or (b) modifies the text referenced by its third argument and returns true (whereupon the error is considered as fixed as possible, so no other remedy will be invoked for this error).

The driver base class parse_string method first tries to use the underlying XML parser to parse the document. If that works, all is well; otherwise, it attempts to apply remedies to fix the problem that arose. It considers each remedy class in turn; as soon as one remedy says it's handled this error, it tries to parse again. If no remedies claim to have handled the error, it gives up.

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