Per the customer's description and rational:

Now my feature request: it would be helpful if as part of a pipeline job definition one could specify the "Stream" by using an environment variable - see
 
p4jenkins_image1.png attached
In this case it would be nice if I could use a folder property like:

 
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Rational behind this: I have some tree of jobs which all relate to a project which is based on a single stream. It is error prone to have this stream name explicit in each job: a symbolic expression pointing some environment variable which is stored as a folder property is better.