Variable names may consist of letters, numbers and the underscore _. They have to start with a letter or the underscore.
var = expr redefines var as the value
Any previous value or data type of var is forgotten. The expr can be a data type, function, file, or any other object.
The = operator is a binary operator which has the side effect of redefining its left operand. It associates to the right, so
var1 = var2 = var3 = expr initializes all three var to expr