34:  How do I control Emacs's case-sensitivity when searching/replacing?

  For searching, the value of the variable case-fold-search determines
  whether they are case sensitive:

    (setq case-fold-search nil) ; make searches case sensitive
    (setq case-fold-search t)   ; make searches case insensitive

  Similarly, for replacing the variable case-replace determines whether
  replacements preserve case.

  To change the case sensitivity just for one major mode, use the major
  mode's hook.  For example:

    (add-hook 'XXX-mode-hook
          (function
           (lambda ()
             (setq case-fold-search nil))))