From http://www.w3schools.com (Copyright Refsnes Data)
Errors in XML documents will stop your XML program.
The W3C XML specification states that a program should not continue to process an XML document if it finds an error. The reason is that XML software should be easy to write, and that all XML documents should be compatible.
With HTML it was possible to create documents with lots of errors (like when you forget an end tag). One of the main reasons that HTML browsers are so big and incompatible, is that they have their own ways to figure out what a document should look like when they encounter an HTML error.
With XML this should not be possible.
To help you syntax-check your xml, we have created an XML validator.
Paste your XML in the text area below, and syntax-check it by pressing the "Validate" button.
You can also syntax-check your XML file by typing the URL of your file into the input field below, and then press the "Validate" button
If you want to validate an error-free XML file, you can paste the following address into the filename field: http://www.w3schools.com/dom/cd_catalog.xml
Note: If you get the error "Access denied" when accessing this file, it is because your browser security settings do not allow access across domains.
From http://www.w3schools.com (Copyright Refsnes Data)