File types with associated preview handlers can be displayed with the standalone viewer using the SHOW command. For example, on my system a .dcf file displays as text and a .pdf file displays as it would look when printed or opened with a PDF application. Some other file types, e.g. .exe, are displayed as hex and unknown file types display an "Unable to load picture" message.
From within a script it would be useful to be able to determine which category a file item falls into - Displayable/Hex/Unknown. Perhaps the ITEM object could be extended to provide this information?