title: Variable-Length Lookbehind not work in perl file, but work in one-liner
body: <p>If I put <code>s/(?&lt;!(?:href|src)=.{0,40})jpg//g</code> in a perl file, and try to run it, it will give the warning: <code>Variable length lookbehind is experimental in regex; marked by</code> and fail.</p>
  <p>But if put in a perl one-liner, it will run successfully, although still be warned of <code>Variable length lookbehind is experimental in regex; marked by</code>.</p>
  <p>Is it by current design or maybe I'm using it wrong?</p>
  <p>Update: I'm using perl 5.31.3</p>