Facebook IFrame App Validating Registration Form Fields

I'm creating a website in C# ASP.NET and I'm trying to integrate Facebook. I've used a Facebook IFrame as my registration form and the Facebook C# SDK here http://facebooksdk.codeplex.com/ to access Facebook user details. So far I've figured out how to add the fields I require in the Facebook IFrame, and using the SDK I know how to decrypt the data posted back to me from the signed request field server side.

My question is how can I add validation to the fields before they are posted? It seems that the password field I've added to the Facebook IFrame registration form already has some validation since the password must be at 开发者_如何学JAVAleast 8 characters, but I'm not sure how this is being done or if/how I can possibly customise it.

Hopefully someone out there can help point me in the right direction. Thanks for reading.

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Sigh! To answer my own question I finally found this documentation here...

http://developers.facebook.com/docs/plugins/registration/advanced

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I've reviewed that documentation and still can't find a way to add custom validations to fields such as 'email'. It appears to me that only custom fields can have validations. Have you experienced this as well?

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Client side validation in registeration plugin is only available in "xfmbl". you cannot perform validation using iframe.. see advance uses of registration plugin..

https://developers.facebook.com/docs/plugins/registration/advanced/

under the heading of Client Side Validation, it clearly states

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If you want to add validation to any of your fields during registration, you must use the XFBML version of the plugin, since the iframe can't do cross domain communication.

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hope it helps...