By default, the FilterBarFor property is empty, which indicates that the thumbnail's caption is what the filter feature is filtering for. You can use the FilterBarFor property to specify data the filter feature is filtering for. The FilterBarVisible property specifies whether the control's filter bar is visible or hidden. Use the Caption property to specify a caption to be displayed on the thumbnail. The SingleCaption property indicates the expression to generate the HTML caption to be displayed on the thumbnail, when the control shows a single thumbnail. 

For instance:

• "fname" filters for file names

The FilterBarFor property supports the following keywords: 

• fcount keyword, returns the number of thumbnail files
• findex keyword, specifies the index of the thumbnail file
• ffile keyword, returns the file
• fname keyword, returns the name of the file
• faname keyword, returns the alternate name of the file, 8.3 format truncated version of the name
• fext keyword, returns the extension of the file
• fcreated keyword, specifies when a file or directory was created (UTC)
• fcreated_local keyword, specifies when a file or directory was created (local date-time)
• fmodified keyword, specifies when a file or directory was last modified (UTC)
• fmodified_local keyword, specifies when a file or directory was last modified (local date-time)
• fopened keyword, specifies when a file or directory was last accessed (UTC)
• fopened_local keyword, specifies when a file or directory was last accessed (local date-time)
• fsize keyword, specifies the size of the file
• fsizeF keyword, returns automatically the size of the file in KB, MB or GB
• ffolder keyword, returns 0, 1, 2, -1 or -2, if the object does not exist, it is a file, a shell item, a folder or a drive
• fattr keyword, returns the attributes of the file/folder
• ftype keyword, returns the type of the file/folder, like JPG File, ...
• fpicture keyword, indicates whether the file points to a known picture type, like BMP, PNG, and so on
• fwidth keyword, returns the width of the picture file
• fheight keyword, returns the height of the picture file
• ffilter keyword, returns the currently filter pattern ( FilterBarPromptPattern property )
• fvcount keyword, indicates the number of visible thumbnails. For instance, if a filter is applied the fvcount returns the number of available/visible/filtered thumbnails.
• fvindex keyword, indicates the index of the thumbnail in the visible collection.

This property/method supports predefined constants and operators/functions as described here.