mktempdir node.... Name problems

[Just-another-pleb]

I have this flow:

[{"id":"1dc13905.7fc907","type":"inject","z":"df652827.d02c3","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":110,"y":3120,"wires":[["fad9e124.79714"]]},{"id":"fad9e124.79714","type":"change","z":"df652827.d02c3","name":"set things","rules":[{"t":"set","p":"log_paths","pt":"global","to":"/home/me/temp","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":280,"y":3120,"wires":[[]]},{"id":"d03383e0.75e908","type":"fs-ops-mktmpdir","z":"df652827.d02c3","name":"temp","path":"log_paths","pathType":"global","prefix":"payload","prefixType":"msg","mode":"777","fullpath":"directory","fullpathType":"msg","x":280,"y":3240,"wires":[[]]},{"id":"ecea9f6a.aff598","type":"inject","z":"df652827.d02c3","name":"","topic":"","payload":"blah","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":100,"y":3240,"wires":[["d03383e0.75e908"]]}]

The name of the directory made is called: blahrbWUi5

Where does the rbWUi5 bit come from?

Not very well explained in the info for the node.