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")

##</code><code>##

               As a special case, specifying a PATTERN of space (' ') will
               split on white space just as "split" with no arguments does.
               Thus, "split(' ')" can be used to emulate awk’s default
               behavior, whereas "split(/ /)" will give you as many null
               initial fields as there are leading spaces.  A "split" on
               "/\s+/" is like a "split(' ')" except that any leading
               whitespace produces a null first field.  A "split" with no
               arguments really does a "split(' ', $_)" internally.