As an add-on, I have my own personal "code" for what the first character means -
@ represents an action type - @Call, @Waiting, @Online, @Computer and so on (@Computer in terms of action means something I need to use a computer for, not a specific location)
~ is specifically for shopping needs, and generally designates a shopping location, sometimes specific, sometimes a generic location, i.e. ~Costco, ~GroceryStore, ~Safeway, ~Amazon, ~Mall
# is a "location" context (other than shopping) - #Office, #Home, #DevComputer, #HomeComputer, #Laptop (#HomeComputer is a specific machine I need to be at, in this case. Yes, it overlaps with the action type @Computer, but they are used for two different things in my setup)
+ is used to denote a person or group of people like +Family, +Eric, +Colleagues, etc.
There are others, but you get the idea.