terrible documentation for data-mapper

[apc300]

this issues list is linked to directly from https://flows.nodered.org/node/node-red-contrib-data-mapper
there is no link on that page which gives any information on how to use that node-red node
google comes up with nothing useful

when trying to use node-red-contrib-data-mapper for the first time there are many questions of what each box is used for and how exactly it uses json to map the data