Specifying master page in Web.config causes every content page to inherit from the master page
<configuration>
<system.web>
<pages masterPageFile="~/Default.master" />
</system.web>
</configuration>
Once specified in this manner, the content page's Page directive can then be :
<%@ Page Language="VB" %>
You can override the application-wide master page specification by
declaring a different master page within your content page:
<%@ Page Language="VB" MasterPageFile="~/MyOtherCompany.master" %>