For anyone following this thread and interested, here's the third
version of the sample code.  This does work:

----
require 'tk'
require 'tkextlib/tkHTML'

def do_click(x,y)
  href = $HTML.href(x,y)[0]
  print href + "\n" if href
end

$HTML = Tk::HTML_Widget.new(TkRoot.new)
Tk::HTML_Widget::ClippingWindow.new($HTML).bind('1',
  proc {|x,y| do_click(x,y)},"%x %y")
$HTML.parse("<a href=foo>click me</a>")
$HTML.pack

Tk.mainloop
----