Every piece of information in a computer program has a type. This is because you can
only do certain things with certain kinds of information. It doesn’t make sense to multiply
two strings together, for example.
The important thing about a type is the operations you can perform on something of
that type.
For now, you just need to know that any description of a command or operation 1 in
the REALbasic documentation will specify what types the arguments to the command
1. An operation is something like + or * in mathematics. The + in our program, that puts
two strings together, is another example.