Python Toolbox - how to create info banner?

[AngusHooper1]

How do we create an info banner in a custom python toolbox? 

The join field geoprocessing tool is a good example of the desired functionality. This gp tool displays a blue info banner with a green text message that "this tool modifies the input table".

Is this exposed as a tool method or property? Or, is this part of the pro sdk?

[DanPatterson]

I messed with one of mine in a custom *.atbx

You need 7zip to edit the compressed archive

right-click on the *.atbx that you created.

then right-click on tool content, select Edit from there NOT the Edit menu on the top

The "key" was to find the key that is used in esri tools which in this case was an "attributes" parameter for the join field tool (input_data_change).

I added it to my tools parameter, saved it and it appears in the 2nd image.

I will have to remove it after gardening 😉