When I use the search box built into Slack, I'm presented with a choice of what channels to include in the search, but the most limited choice I can make there is "Include: only messages from channels that I have opened". This is very inconvenient considering 99% of times I know very well which channel (or "DM channel") the message is in (usually it's a "DM channel").
How do I search in a single channel (which may be a "DM channel")?
Note: I don't know if there's an official name for "DM channels", I use this term to mean "the space where I exchange messages with a single person".