ASP.NET – Do you have multiple scriptManagers? If so, what condition is needed?

Can a page have multiple ScriptManagers? If yes, under what conditions?

MSDN says no, you cannot have more than one (emphasis mine):

A page can contain only one ScriptManager control in its hierarchy. To register services and scripts for nested pages, user controls, or components when the parent page already has a ScriptManager control, use the ScriptManagerProxy control. For more information, see Using the ASP.NET UpdatePanel Control with Master Pages