If an overlay has a @code{help-echo} property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window. For details see @ref{Text
-help-echo}. This feature is available starting in Emacs 21.
+help-echo}.
@item modification-hooks
@kindex modification-hooks @r{(overlay property)}
You can alter the way help text is displayed by setting the variable
@code{show-help-function} (@pxref{Help display}).
-This feature is used in the mode line and for other active text. It is
-available starting in Emacs 21.
+This feature is used in the mode line and for other active text.
@item keymap
@cindex keymap of character