53:  How do I insert `>' at the beginning of every line?

  To do this to an entire buffer, type "M-x replace-regexp RET ^ RET >
  RET".

  To do this to a region, use "string-rectangle" ("C-x r t").  Set the mark
  (`C-SPC') at the beginning of the first line you want to prefix, move the
  cursor to last line to be prefixed, and type "C-x r t > RET".  To do this
  for the whole buffer, type "C-x h C-x r t > RET".

  If you are trying to prefix a yanked mail message with '>', you might
  want to set the variable mail-yank-prefix.  Better yet, get the SuperCite
  package (see question 103), which provides flexible citation for yanked
  mail and news messages.