Hi,
Thanks for the question. Please take a look at the attached file. I've nested the Pickets Generator inside the Posts Rails generator as a default segment. I've also combined it with the existing Railings segment using a Compose operator. The X Size of both of those is set using an expression that finds the available space on a spline section, as follows:
return Posts_Rails.XSectionAdjustedLength;
I hope that helps, please let me know if you have any further questions.
Cheers,
Paul