I found that RDoc generate a dangling hyperlink.

For example, RDoc generates a hyperlink to classes/M.html which is not
exists as follows.

% cat a.rb 
module M
  def m1() end

  # :stopdoc:

  def m2() end
end
% rdoc a.rb

                               a.rb: m.
Generating HTML...

Files:   1
Classes: 0
Modules: 1
Methods: 1
Elapsed: 0.068s
% grep m1 doc/**/*(.)
doc/classes/M.src/M000001.html:    m1 (M)
doc/classes/M.src/M000001.html: <title>m1 (M)</title>
doc/classes/M.src/M000001.html:  <span class="ruby-keyword kw">def</span> <span class="ruby-identifier">m1</span>() <span class="ruby-keyword kw">end</span></pre>
doc/fr_method_index.html:               m1 (M)<br />
% ls doc/classes/M.html
ls: doc/classes/M.html: No such file or directory

Since the following description in lib/rdoc/README, it is not problem
that classes/M.html is not exist.  But I think the dangling hyperlink
is a problem.

    [<tt>:stopdoc: / :startdoc:</tt>]
         Stop and start adding new documentation elements to the
         current container. For example, if a class has a number of
         constants that you don't want to document, put a
         <tt>:stopdoc:</tt> before the first, and a
         <tt>:startdoc:</tt> after the last. If you don't specifiy a
         <tt>:startdoc:</tt> by the end of the container, disables
         documentation for the entire class or module.
-- 
Tanaka Akira