An expression is a sequence of variables, constants, operators, functions, and parentheses following algebraic rules that calculates a value. Expressions and their intermediate results must be representable as character strings of less than 256 characters.
Every value (in variables, constants, or the result of expressions) has a data type. As form calculates an expression, it propagates or converts the data type of values as appropriate. For example, "5" + 10 evaluates to 15 of data type real. The string "5" is converted to real so it can be added to 10.