XML Parsers

What is a parser? It's a piece of software whose job description is to check that an XML document is valid or, failing that, well-formed. Not very interesting to the average user, perhaps, but a vital part of the picture if validity and well-formedness are to have any real meaning in the XML world.
Any software package that is XML-aware will have a parser built into it in the form of an XML processor. As a minimum, the XML processor checks the XML documents you are about to work on, and checks them again when you have finished. Ideally, it is interactive; any errors you introduce are reported and can be sorted out while you work.

You also can get standalone XML parsers, which are important if you take the plain text editor route for your XML authoring. When you have finished working on an XML document in an uncontrolled environment (one that doesn't know about XML tagging conventions), you should always run an XML parser on it to check that it is still valid.

Kinds of parsers
There are several different ways to categorize parsers: