Markers and Alt text

Hi everyone,

I have a question about markers and alt text:

I am building a course where I have markers positioned over screenshots of Word to explain certain functionalities. 

My understanding is that when you tab to a marker, the screen reader instructs you to press the spacebar (or enter) to activate the marker. However, I also wanted to give learners information on where the marker is positioned over the screenshot, to give them context (e.g. Marker positioned over MS Word Review tab).

Would it be OK for me to add this information in the marker's alt-text field? Will the screen reader read both the alt-text and the text in the marker's label, or will the screen reader only read the alt-text? 

Thank you in advance!