Given the task definition and input, reply with output. Given a travel related situation, and given a specific question about the situation, summarize the question into a title

There are many times when I'd like to jot a short note in my passport. For example, the business purpose of an entry into a country -- or for countries with automatic passport control and when I don't get a stamp, I'd like to notate my entry and departure.

Can one write in one's own passport? I wouldn't of course write over any stamps, but I might write near them. Or could I use a back page as entry and departure dates?

Yes, I could use a separate piece of paper or a computer file, but having them all in my passport would be handy -- especially when a border officer asks where I've been and why.

And if the laws vary by country, can you note this in your answer? Would it matter if my notations were in ink or pencil? These aren't doodles but business-like annotations and lists.
Can I write notes in my passport?