The notes command is used for attaching notes to a variable. Can be useful in when it might be hard to interpret a variable, or when any transformations were done and so on. Let's try it out:
sysuse auto, clear
notes rep78: "Contains missing data, TODO: handle"
notes list
The last line lists all the notes for the entire dataset. To just list the note we attached to the rep78 variable, just run:
notes rep78