About an Expression

An Expression is composed of operands and operators. It may be edited in one of the following ways:

Typed inline: type the expression in the Expression property box. By using the drop-down list, you can access the variables declared so far.
Use the Expression editor: to launch this editor, simply use the drop-down in the Expression property box, or double-click the Expression property or the widget element itself.

Your eSpace is only valid if all the expressions are also valid. See how to verify an expression.

Handling an expression

There are many functions to manipulate the type Text, but the only operand that can be used directly over text is "+", which concatenates the left operand (string) with the right operand (also a string).
You cannot use any of the numeric operators to handle the types Date, Time, and DateTime. There are specific built-in functions to handle these types.
You cannot make any calculation on the type BinaryData.
You cannot make any calculation on the type Identifier. There are specific built-in functions to handle this type.
You can only use the operators "=" and "<>" for the type Record.
You cannot make any calculations on the type Record List.
You can define and use your own functions by setting the Function property of your user-defined actions.

When expressions in widgets are evaluated

Expressions in widget properties are normally evaluated when the widget is being rendered. Exceptions are:

The expressions used in the Source Record property of an Edit Record widget are only evaluated when the web screen is loading, immediately after the Screen Preparation.

Source Record is always evaluated, even when the widget is inside an If widget.

The expressions used in the Source Record and Source Record List properties of the widgets Show Record, List Records, and Table Records are evaluated in screen rendering time, when a widget runtime property is first used (e.g. an expression that uses the runtime property Length of a List Records widget) or when it is rendered.
The expressions used in the Start Index property of the widgets List Records and Table Records are evaluated before the preparation.
The expressions in arguments of the widgets Buttons or Links with Method equal to Submit, are evaluated when the button or link is pressed.
The expressions in arguments of the widgets Buttons or Links with Method equal to Ajax, are evaluated when the button or link is pressed.