What are the valid elements and attribute values I should use in an XML file?

For a Struts 2 application I have used validations using the validation.xml.

In that I use various elements. How do I kn开发者_如何学编程ow what are the elements, subelements are there, and what are the attributes for them, what are the values I should use for the attributes?

I have looked in the DTD URL mentioned in DOCTYPE but there is no detailed information about the elements.

I would suggest to try several IDE plug-ins that support Struts 2 (e.g. IntelliJ too - even if it's commercial - there's a 30 days trial). If your project is setup correctly then they should offer supplemental hints when editing those files (for example, code completion hints, error highlighting for bad attributes, etc.) - that's much faster than digging in incomplete documentation.

I know, this is not the conventional/correct way of learning things, but these days IDEs are so smart that, at least for me, I can say I learn a lot from them :).