Set the filter pattern for the file requester. Only files which match this filter pattern will be
selectable in the requester. The filter pattern is a string that contains a number of file extensions
that will be accepted by the requester. These endings must be separated by '|' characters. For example:
"voc|wav|8svx|16sv|iff|aiff" will only show files which have one of these extensions.
If you don't set this attribute, all files will be selectable.