Question : wpf validation xaml textbox

Hi experts,

I'm new to wpf and xaml. I am familiar with C# and windows forms.  

Does anyone one know the link to a good tutorial on WPF xaml validation?

For example say i have 2 textboxes, one is for username and one is password the once they are entered they then press the login button.  This username and password is checked with values in sql server and if they are valid they are then taken to the main window.

I just want to validate what the user enters into the textboxes. Like for example, make sure the textboxes are not left blank or only 8 digits for the username are entered.

I know xaml offers some good validation tools built into controls, i just need an nice example using validation with xaml since i'm new to xaml.

Thanks for any help on you can give me.

Answer : wpf validation xaml textbox

Hello, this articles were helpfull for me:
http://www.silverlightshow.net/items/Data-Validation-in-Silverlight-3.aspx
http://msdn.microsoft.com/en-us/magazine/ee335695.aspx

And you can also take a look at this validation framework:
http://silverlightvalidate.codeplex.com/