The Item: Viewer
A Viewer is an item used to display a file contents.
By default, the program used to display the file contents is the program specified in the general preferences (menu options). However, it is possible to specify a particular program for each viewer by the way of the related property dialog.
For example, any text editor is fine to display text files (e.g. gedit, NotePad), or any image viewer is fine to display image file (eg. Paint, Gimp). However, this program should be accessible as command line.
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