By default, the CustomFilter property is empty. The CustomFilter property has effect only if it is not empty, and the FilterType property is not exImage, exCheck or exNumeric. Use the DisplayFilterPattern property to hide the text box to edit the pattern, in the drop down filter window. The All predefined item and the list of custom filter is displayed in the drop down filter window, if the CustomFilter property is not empty. The Blanks and NonBlanks predefined items are not defined, when custom filter is displayed. Use the Description(exFilterBarAll) property on empty string to hide the All predefined item, in the drop down filter window. Use the DisplayFilterButton property to show the button on the column's header to drop down the filter window. Use the Background property to define the visual appearance for the drop down button.

The CustomFilter property defines the list of custom filters as pairs of (caption,pattern) where the caption is displayed in the drop down filter window, and the pattern is get selected when the user clicks the item in the drop down filter window ( the FilterType property is set on exPattern, and the Filter property defines the custom pattern being selected ). The caption and the pattern are separated by a "||" string ( two vertical bars, character 124 ). The pattern expression may contains multiple patterns separated by a single "|" character ( vertical bar, character 124 ). A pattern may contain the wild card characters '?' for any single character, '*' for zero or more occurrences of any character, '#' for any digit character. If any of the *, ?, # or | characters are preceded by a \ ( escape character ) it masks the character itself. If the pattern is not present in the (caption,pattern) pair, the caption is considered as being the pattern too. The pairs in the list of custom patterns are separated by "|||" string ( three vertical bars, character 124 ). So, the syntax of the CustomFilter property should be of: CAPTION [ || PATTERN [ | PATTERN ] ] [ ||| CAPTION [ || PATTERN [ | PATTERN ] ] ]. 

For example, you may have a list of documents and instead of listing the name of each document in the filter drop down list for the names column you may want to list the following:

Excel Spreadsheets
Word Documents
Powerpoint Presentations
Text Documents

And define the filter patterns for each line above as follows:

*.xls
*.doc
*.pps
*.txt, *.log

and so the CustomFilter property should be "Excel Spreadsheets (*.xls )||*.xls|||Word Documents||*.doc|||Powerpoint Presentations||*.pps|||Text Documents (*.log,*.txt)||*.txt|*.log". The following screen shot shows this custom filter format: