+Text inside the @samp{%<} and @samp{%>} specifiers will get the special
+@code{balloon-help} property set to @code{gnus-balloon-face-0}. If you say
+@samp{%1<}, you'll get @code{gnus-balloon-face-1} and so on. The
+@code{gnus-balloon-face-*} variables should be either strings or
+symbols naming functions that return a string. Under @code{balloon-help-mode},
+when the mouse passes over text with this property set, a balloon window
+will appear and display the string. Please refer to the doc string of
+@code{balloon-help-mode} for more information on this.
+