title: how can I diff two sections of the same file?
body: <p>I have a source file with two similar yet subtly different sections.  I'd like to merge the two sections into one subroutine with a parameter that handles the subtle differences, but I need to be sure I'm aware of them all so I don't miss any.<br>
  What I usually do in such cases is copy each of the sections to a separate file and then use tkdiff or vimdiff to highlight the differences.  Is there any way to skip the intermediate files and just diff two parts of the same file?</p>