DB<140> s/x/$a.'.'.$a/ree      # -> eval "\$b.\$b"
 => "BB"

  DB<141> s/x/$a.'.'.$a/re       # -> eval '$a.\'.\'.$a'
 => "\$b.\$b"

  DB<142> s/x/$a.'.'.$a/r        # -> "$a.'.'.$a"
 => "\$b.'.'.\$b"

  DB<143> eval "\$b.'.'.\$b"     # what perldoc predicts for line 140
 => "B.B"