title: Convert positive lookahead regex to negative lookahead one?
body: <p>as the title goes, I want to change the script containing positive lookahead into negative one.</p>
  <p>my script is</p>
  <p><code>^[^\S\n]*\n(?=[^\n]*\S)</code>
  of course it needs to be identical in search task.</p>
  <p>the reason to do this is my text editor does not allow replace one by one task for script containing positive lookahead, instead it only allows replace-all.</p>