New Features for Defining Commands

• If the interactive specification begins with `@', this means to select the window under the mouse. This selection takes place before doing anything else with the command. You can use both `@' and `*' together in one command; they are processed in order of appearance.
• Prompts in an interactive specification can incorporate the values of the preceding arguments. Emacs replaces `%'-sequences (as used with the format function) in the prompt with the interactive arguments that have been read so far. For example, a command with this interactive specification

  (interactive "sReplace: \nsReplace %s with: ")
  

  prompts for the first argument with `Replace: ', and then prompts for the second argument with `Replace foo with: ', where foo is the string read as the first argument.
• If a command name has a property enable-recursive-minibuffers which is non-nil, then the command can use the minibuffer to read arguments even if it is invoked from the minibuffer. The minibuffer command next-matching-history-element (normally bound to M-s in the minibuffer) uses this feature.