perpendicular connections between parallel flowchart subgraphs

[goyalyashpal]

Discussed in https://github.com/orgs/mermaid-js/discussions/4352

^{Originally posted by goyalyashpal April 27, 2023}

I want to make:

1. perpendicular connections between multiple parallel flowchart subgraphs. or say
2. sequence-diagram styled perpendicular connections between flowcharts. or say,
3. flowchart styled node shapes and "inter actor" arrows in sequence-diagrams.

<sup>* these all are different ways to say the same thing - atleast to me. it's not a multitude of different things and ever increasing demands
* perpendicular lines that is: horizontal lines on TB & verticle lines on LR</sup>

I am thinking of something like the following:

the black lines is just there to indicate similarity with sequence-diagram