bpo-35054: Add yet more index entries for symbols. (GH-10121)

diff --git a/Doc/library/tkinter.rst b/Doc/library/tkinter.rst
index d9c1c35..4af4b73 100644
--- a/Doc/library/tkinter.rst
+++ b/Doc/library/tkinter.rst
@@ -262,6 +262,8 @@
 *classCommand*
    denotes which kind of widget to make (a button, a label, a menu...)
 
+.. index:: single: . (dot); in Tkinter
+
 *newPathname*
    is the new name for this widget.  All names in Tk must be unique.  To help
    enforce this, widgets in Tk are named with *pathnames*, just like files in a