13.10.5 Displaying operator and highlighted arguments in echo area

If the command Function Arglist Displayer is passed a prefix argument, for example by Ctrl+U Ctrl+` then it does not raise a displayer window, but instead displays the operator and its arguments, with highlight, in the Echo Area. This display is interface-specific, and implemented only for the Editor and other tools based on the editor.

LispWorks Release Notes and Installation Guide - 23 Dec 2011