Hi All,
For the composer I engrave for, the hairpin with a dashed section is used when transitioning between two dynamic levels, but there is a rest or silence in the line, and it is a way of reminding the performer that the cresc or decresc continues but to be aware of the rest and not carry the volume through it. This is by no means a universal or accepted convention. It's what my colleague refers to as over specifying notation, to make sure that as things get lost in performance as much as possible of the notated meaning is captured.
Will try your code Stefano, thanks.