Prompt for a regexp, and <del>print the number of matches</del> <ins>delete each line that contains a match</ins> for <del>it in</del> <ins>it, operating on</ins> the <del>buffer</del> <ins>text</ins> after point.  <del>If</del>  <ins>When</ins> the <del>region is active, this operates on</del> <ins>command finishes, it prints</ins> the <del>region instead.</del> <ins>number of deleted matching lines.</ins>