Git tool `tig`: What do these letters mean on the chart?

Question

When I start tig, I see a graph of branches. He uses the letters on these lines to show what happened there:

• "o" means commit
• "M" is a merger
• "I" is a merger

What is the difference between "M" and "I"?

Answer 1

I am marked as initialin tig source code

It seems he marks the initial fixation (common ancestor) of the merger. M indicates a fusion fixation.