Use this formula to hide pieces of Notes documents if the current user is a Web client:
And this to hide if the current user is a Notes client:
You can also use this to control when subforms are displayed. For example, you can have a "web footer" subform which you only want displayed when documents are shown on the web. In the design of the form for the documents, you would do a Create/InsertSubform with "Insert subform based on formula" and a formula of:
@If(@IsMember("$$WebClient"; @UserRoles); "web footer"; "")
In Notes 4.6, there is a special text attribute you can set to hide parts of a document from web users or Notes 4.6 users.