The Expression editor allows you to type and edit expressions in your application module.
The areas and elements available in the Expression editor are presented below:
The top window pane. In this area, you edit your expression by:
Typing the expression directly;
Right-click on the typed expression and select the "Auto Complete" or use CRTL + Space to complete your expressions. Development environment provides you a drop-down list with the possible elements, based on what you typed so far. Therefore you don't have to actually type the complete expression.
In addition, if you want to use a compound element, such as a Widget, Site Property or a Session Variable, select respectively, the widget name, Site or Session followed by ".", and the development environment automatically displays a drop-down list with the runtime properties or the variables;
In this situation, the element you selected in the drop-down list is automatically highlighted in the Scope tree and you can check its definition and help text by:
Using the operator buttons and the elements in the Scope tree, such as Variables or Built-in Functions.
If you want to check the definition or the
help text of any element, place the cursor over the element, right-click
and then select the 
Synchronize Scope Tree option or simply press CTRL
and click the expression.
Contains all the operators handled by the development environment. Learn more about the Expression Operators.
In this area you can access all the elements that can be used in your expression in the current scope. These elements are organized by folders. Learn more about the Scope Tree.
This area contains a description of the currently selected element, which is the value of the Description property of the element. The description includes:
The data type of the function output, that is, in the case of the user functions, the data type of the output parameter;
The description of the function. Built-in functions' descriptions are always provided by the development environment. User functions present the text in the Description property of the user-defined action;
The list of the input parameters, their Is Mandatory and Data Type properties as well as their Description property if not empty.
The Close button closes the expression editor.
Instead of pressing the Close button to accept expression changes, you can press Shift + ENTER or Ctrl + ENTER.
The Help button opens a contextual topic of the OutSystems help.
See Also
Scope Tree | About an expression | Expression Operands | Expression Operators