This can be useful both when revisiting expressions that you'd written some time ago, and also help othe solution builders who may need to maintain, modify the expression in understanding what they do.
Comments ar added be using a # character at the start of the line. If you're comment spans multiple lines then you must use a # character on each line.
# Retrieves the name of the engineer and records it
# for audit purposes as the originator of the fault
=INFO("user.firstname") & " " & ("user.secondname")