Konqueror can also serve as a viewer for a lot of file types. Click on an image and it will display the image in the current view. Click on a text file, it will show its contents. Same for postscript and DVI files, KOffice files, and others.
On the technical side, the very nice thing about this is that those viewers are not part of Konqueror and haven't been developed specifically for it.
Konqueror embeds components (parts) provided by other applications. The image-viewing part is KView, the text-viewing part is KWrite, the DVI viewer KDVI, the PostScript viewer KGhostview, and of course all KOffice documents are shown by their originating application.
Any new type of file you want to be able to display inside Konqueror, you just need to write a part and register it with a desktop file. No need to touch Konqueror in any case. Embedding parts from other applications is provided by the library called KParts.
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