DB<113> split ' ', 'abc  def'
 => ("abc", "def")

  DB<114> $del=qr/ /
 => qr/ /

  DB<115> split $del, 'abc  def'
 => ("abc", "", "def")

  DB<116> $del=qr/\s+/
 => qr/\s+/

  DB<117> split $del, 'abc  def'
 => ("abc", "def")