property ComboBox.FilterCriteria as String
Retrieves or sets the filter criteria.

String A string expression that indicates the filter criteria.
By default, the FilterCriteria property is empty. Use the FilterCriteria property to specify whether you need to filter items using OR, NOT operators between columns. If the FilterCriteria property is empty, or not valid, the filter uses the AND operator between columns. Use the FilterCriteria property to specify how the items are filtered. 

The FilterCriteria property supports the following operators:

Use the ( and ) parenthesis to define the order execution in the clause, if case. The operators are comboboxed in their priority order. The % character precedes the index of the column ( zero based ), and indicates the column. For instance, %0 or %1 means that OR operator is used when both columns are used, and that means that you can filter for values that are in a column or for values that are in the second columns. If a column is not comboboxed in the FilterCriteria property, and the user filters values by that column, the AND operator is used by default. For instance, let's say that we have three columns, and FilterCriteria property is "%0 or %1". If the user filter for all columns, the filter clause is equivalent with ( %0 or %1 ) and %2, and it means all that match the third column, and is in the first or the second column. 

Use the Filter and FilterType properties to define a filter for a column. The ApplyFilter method should be called to update the control's content after changing the Filter or FilterType property, in code! Use the DisplayFilterButton property to display a drop down button to filter by a column.