Use the X-Function edit box to name the X-Function.
Use the Variables pane to specify variable names and labels, data types, default values, etc. To add, insert or delete variables, right-click to the left-side of the pane (see the picture below) and choose from the shortcut menu.
Specify the name of the variable. When the X-Function is executed by script, you have to assign values to variables using their names. Therefore, we recommend that you use shorter names and begin them with different characters.
Specify a label for the variable. Special characters and white space are allowed.
Specify whether the variable is used for input, output or both.
Specify the variable data type.
Specify the default value for the variable.
Specify the control for the variable in the dialog box (combo box, slider, etc.).
Specify an option string for the variable. You can apply advanced settings with option strings, such as grouping several variables together, enabling recalculation, etc. More details can be refered to X-Function Programming CHM.