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The  Microsoft.SharePoint.WebControls  namespace of the   Microsoft.SharePoint.dll  contains a number of validation controls that can be used on application pages and web parts to validate user entry in the SharePoint controls. The different validation controls are: InputFormRequiredFieldValidator InputFormRangeValidator InputFormCompareValidator InputFormRegularExpressionValidator InputFormCheckBoxListValidator InputFormCustomValidator If you want to use these SharePoint control validators, you have to add a page directive to the page: <%@ Register TagPrefix="spuc" Namespace="Microsoft.SharePoint.WebControls"              Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %> The following sections describe the use of the different SharePoint validation controls. The InputFormRequiredFieldValidator control This control inherits from the standard ASP.NET  RequiredFieldValidator