blink

Selected line objects shall blink smoothly. While blinking, minimum line width is 3.

$line blink on: sets tag blink, so line flashes
$line blink off: removes tag blink, so no flash

obj method line blink {{onoff on}} {
  set tag line$self
  if {$onoff} then {
    $self canvas addtag blink withtag $tag
    $self canvas itemconfigure $tag -width [max 3 [$self cget -width]]
  } else {
    $self canvas dtag $tag blink
    $self updateAtts
  }
}