OK, you could also use a vile conventional highlighter, but it has much more style with this elegant filler, which is excellent by the way in hand, working.
Note that the font weight of the filler is not as wide as in conventional highlighters, but I feel that rather than benefit. One can highlight or emphasize a much more targeted.
The highlighter is filled like an ordinary piston filler. Behind the handle turn until the plunger is fully down, turn spring into Tintenglas and opposite to earlier until the punch is at the top.