Mask

You can use the mask to select which kind of files you want to load. You can use the Microsoft Windows wildcards: * for a series of characters and ? for one character. You can use several masks at once by listing them separated by a semicolon (;), comma (,) or space. Every mask adds to the selected list of files. A mask takes effect after you click in another field away from the Mask field, or press Enter.
Note that the mask determines which files are shown in the Files box and thus which files can be selected to load.