Sorry if everyone else knows about this stuff, but I can't find any information about it anywhere.
I see occasional comments about one user putting something on another user's "talk page". I have some questions for a particular user that don't rise to the level of an official question (but it's not a private matter), so I'd like to use this feature. But I can't find it anywhere. What is it? Does it just mean that someone has opened a chat and invited or tagged the other user or something like that? (If so, are there best practices for that?) Or are they friends in some other venue?
My reason for asking this is that I really like one person's formalism and want to ask that particular person for references the she/he uses.
To be clear, I understand that chat exists, but I particularly want this one person's input, and it looks like chat doesn't really have a mechanism for that. I certainly don't mind if other people chime in with their opinions about references, but I would like to ask one person in particular.