Going through the sample

BranchFlow

in the Outerbounds Metaflow online demo, I tried to see how I can transfer my own variables to each step. Can someone explain to me why

join()

is not able to see

y

from

start()

? Is there some sort of rule I'm missing when it comes to retaining inputs and outputs from step to step? Also, is there a way to pass a variable without using

self

? From the documentation I read, I think that all variables in Metaflow are tracked. What if there was some "filler" or "intermediary" value that wasn't significant to the entire flow that a user does not wish to track? How do we pass this value to the next step?