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(elisp)Comparing Text

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Comparing Text
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   This function lets you compare portions of the text in a buffer,
without copying them into strings first.

 - Function: compare-buffer-substrings buffer1 start1 end1 buffer2
          start2 end2
     This function lets you compare two substrings of the same buffer
     or two different buffers.  The first three arguments specify one
     substring, giving a buffer and two positions within the buffer.
     The last three arguments specify the other substring in the same
     way.  You can use `nil' for BUFFER1, BUFFER2, or both to stand for
     the current buffer.

     The value is negative if the first substring is less, positive if
     the first is greater, and zero if they are equal.  The absolute
     value of the result is one plus the index of the first differing
     characters within the substrings.

     This function ignores case when comparing characters if
     `case-fold-search' is non-`nil'.  It always ignores text
     properties.

     Suppose the current buffer contains the text `foobarbar
     haha!rara!'; then in this example the two substrings are `rbar '
     and `rara!'.  The value is 2 because the first substring is greater
     at the second character.

          (compare-buffer-substrings nil 6 11 nil 16 21)
               => 2