A symbol may possess any number of symbol properties, which
can be used to record miscellaneous information about the symbol. For
example, when a symbol has a risky-local-variable property with
a non-nil value, that means the variable which the symbol names
is a risky file-local variable (see File Local Variables).
Each symbol’s properties and property values are stored in the symbol’s property list cell (see Symbol Components), in the form of a property list (see Property Lists).