Clarify 'displayof' option

Author: E-Paine

Doc/library/tkinter.font.rst

@@ -48,14 +48,15 @@ The different font weights and slants are:
    .. method:: actual(option=None, displayof=None)
 
       Returns the actual value for attributes when the given font is used on
-      *displayof*. Due to some differences between operating systems (such as
+      the widget given by *displayof*. *displayof* accepts any tkinter widget
+      and, if omitted, will default to the main window (in most circumstances,
+      this will be your ``Tk`` instance).
+
+      Due to some differences between operating systems (such as
       pointsizes and the availability of font families), some values returned
       by this method may vary from those given as kwargs or similar method
       (and retrieved by :meth:`Font.cget`).
 
-      *displayof* accepts any tkinter widget and, if omitted, will default to
-      the main window.
-
       If *option* is specified, the value of just that attribute is returned.
       If it is omitted or ``None``, the returned value is a dictionary of all
       the attributes and their values. See above for a list of acceptable