code: def remove_entity_headers(headers, allowed=("content-location", "expires")):
      
      allowed = set([h.lower() for h in allowed])
      headers = {
          header: value
          for header, value in headers.items()
          if not is_entity_header(header) or header.lower() in allowed
      }
      return headers
docs: Removes all the entity headers present in the headers given.
      According to RFC 2616 Section 10.3.5,
      Content-Location and Expires are allowed as for the
      "strong cache validator".
      https://tools.ietf.org/html/rfc2616#section-10.3.5
  
      returns the headers without the entity headers