Editing Object Linking and Embedding (section)

===OLE custom controls===
OLE custom controls were introduced in 1994 as a replacement for the now deprecated Visual Basic Extension controls. Instead of upgrading these, the new architecture was based on OLE. In particular, any container that supported OLE 2.0 could already embed OLE custom controls, although these controls cannot react to events unless the container supports this. OLE custom controls are usually shipped in the form of a [[dynamic link library]] with the .ocx extension. In 1996 all interfaces for controls (except IUnknown) were made optional to keep the file size of controls down, so they would download faster; these were then called [[ActiveX Control]]s.