In an experimental Python AddIn that I've created using ArcPy from ArcGIS 10.3.1 for Desktop I have put some test help into my config.xml for a button called Button4:
<Button caption="Button4" category="Experimental Addin" class="ButtonClass6" id="Experiment_addin.button4" image="" message="Button4 Message goes here" tip="Button Tip goes here">
<Help heading="Button4 Help Heading goes here" Content="Button4 Help Content goes here" />
When I make and install my Python AddIn, the message and tip show up by mousing over the button as expected.
However, I have not figured out how to invoke the Help Heading and Content mentioned in Creating a Python add-in tool:
The final section of the tool is the help heading and content. These properties allow you to supply information that appears when a user invokes context-sensitive help. These are pop-up topics that remain on-screen until the user clicks somewhere else.
Prior to 10.1 I know that this could be done using the now deprecated What's This button, but how is context-sensitive help invoked since 10.1?
I thought it might have been by mousing over the button and hitting F1, but that does nothing. If I mouse over anything but a toolbar and hit F1 it brings up the ArcGIS 10.3.1 Help.