Validation and Invalidation in flex

I am new in flex and recently read about Validation and Invalidation in components. May somebody explain what it's mean and when it's use, may be some good article.开发者_开发技巧

some links for you to learn http://livedocs.adobe.com/flex/3/html/validators_2.html

http://blog.flexexamples.com/2007/08/13/validating-flex-forms-using-the-validator-classes/

I think the chapter "About creating advanced components" from the Adobe Flex LiveDocs will be a good starting point. Take notice of the subchapter "About the invalidation methods".