An important concept of Field Visualization is distinguishing the value of the field from its current visualization. It is possible for a field value to be set to a value that is not compatible with how that field is currently visualized. In this case the field variable and its visualization will be different.
Example. Define a field called SEX(Alpha(1)). Add a picklist and two picklist items to the field from its component source. Set captions and values for the two picklist items. Visualize the field as a ButtonSet on a form.
For the above scenario code can be compiled that allows the setting of the field to any value even though the Visualization for that field will only respond correctly to being changed to a value in the picklist.
The NoMatchAction property of the Picklist should be used in this case to define the behavior to be taken by the Visualization.
As the name suggests, this feature is related to the appearance of a field, and does not necessarily affect the value of the underlying variable at run time. The Visualization will attempt to show the value of the field where possible. However, it is possible to have a value in the underlying variable that is NOT in the PICKLIST.