Append Completion registry parameter allows to control the auto complete behavior of IE when user begins to type in URL address. This registry parameter is present under the key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerAutoComplete.
Append Completion is of type REG_SZ and takes the values yes or no. When setto yes, whenever user starts to type in some URL, internet explorer tries to guess the complete URL based on the previous browsing history of the user and suggest the same to the user.
For example, when I typed in windows, IE automatically figured out technlg.net/windows/ based n my previous history and suggested the URL as shown in the above snapshot.