What does Length mean in Qto_StairFlightBaseQuantities?

https://forums.buildingsmart.org/t/what-does-length-mean-in-qto-stairflightbasequantities/3668

The description from the docs is:

> Total length of the stair flight along the walking line.

Can someone draw a diagram of this for clarification? There are perhaps a few equally valid interpretations here.

Start with the linked buildingSMART forum discussion and the quoted documentation for Qto_StairFlightBaseQuantities. Determine which interpretations of “total length” along the walking line are under discussion, then prepare a diagram and clarification that resolves the ambiguity in the IFC4.x specification.

Written by the indexing model from the issue text.