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(elisp)Internals of Kill Ring

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Internals of the Kill Ring
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   The variable `kill-ring' holds the kill ring contents, in the form
of a list of strings.  The most recent kill is always at the front of
the list.

   The `kill-ring-yank-pointer' variable points to a link in the kill
ring list, whose CAR is the text to yank next.  We say it identifies
the "front" of the ring.  Moving `kill-ring-yank-pointer' to a
different link is called "rotating the kill ring".  We call the kill
ring a "ring" because the functions that move the yank pointer wrap
around from the end of the list to the beginning, or vice-versa.
Rotation of the kill ring is virtual; it does not change the value of
`kill-ring'.

   Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables
whose values are normally lists.  The word "pointer" in the name of the
`kill-ring-yank-pointer' indicates that the variable's purpose is to
identify one element of the list for use by the next yank command.

   The value of `kill-ring-yank-pointer' is always `eq' to one of the
links in the kill ring list.  The element it identifies is the CAR of
that link.  Kill commands, which change the kill ring, also set this
variable to the value of `kill-ring'.  The effect is to rotate the ring
so that the newly killed text is at the front.

   Here is a diagram that shows the variable `kill-ring-yank-pointer'
pointing to the second entry in the kill ring `("some text" "a
different piece of text" "yet older text")'.

     kill-ring                  ---- kill-ring-yank-pointer
       |                       |
       |                       v
       |     --- ---          --- ---      --- ---
        --> |   |   |------> |   |   |--> |   |   |--> nil
             --- ---          --- ---      --- ---
              |                |            |
              |                |            |
              |                |             -->"yet older text"
              |                |
              |                 --> "a different piece of text"
              |
               --> "some text"

This state of affairs might occur after `C-y' (`yank') immediately
followed by `M-y' (`yank-pop').

 - Variable: kill-ring
     This variable holds the list of killed text sequences, most
     recently killed first.

 - Variable: kill-ring-yank-pointer
     This variable's value indicates which element of the kill ring is
     at the "front" of the ring for yanking.  More precisely, the value
     is a tail of the value of `kill-ring', and its CAR is the kill
     string that `C-y' should yank.

 - User Option: kill-ring-max
     The value of this variable is the maximum length to which the kill
     ring can grow, before elements are thrown away at the end.  The
     default value for `kill-ring-max' is 30.