In the BlueCoat Proxy SG CPL you can write this code
request.header.Referer.url.category=""WhiteList","Education","Government/Legal","Health","Reference","Web Ads/Analytics"" Allow ;
This means that when a website is accessed that is on your custom whitelist or any of the above categories, content that page refers you to is also allowed eg: a Clinical training website classified as Health or Education which has youtube videos embeded on the page.
This allows you to block youtube for your users, but allow them to use that content when it has been referred to by a whitelisted/approved site.
Which stops pages half loading due to cross domain content, or popup prompts on pages which are whitelisted, but cross domain content hasnt been.
However, when writing this code in the VPM visual policy manager, it replaces request.header.Referer with request.x_header.Referer to signify a custom header, which causes this rule to no longer function as the referer isnt a custom HTTP header.
My feature request would be to allow the VPM to create this as a standard header type rather than a custom type.