Sequence Diagram Combined Fragments


i have a question related to combined fragments (alt., loop etc.) in sequence diagrams. Whenever i select “Always show model element indicators” in the diagram’s presentation option, letter “M” is presented just below the alt or loop indicator. I would be grateful if you could let me know what this letter means…

Thank you,

It standards for “master view”, and there is auxiliary view for a model element. You can get to know more with this link: