Coordination with other projects may solve some of these issues. Agents are responsible for retrieving documents over the network. There are HTTP agents, Gopher agents, FTP agents, etc. Viewers display a document in a certain format. Because of W3A, all viewers display their output through Argo, which means that the user notices no difference.
Filters convert documents from one format to another.
For example, when there is a good viewer applet available for GIF, but not for TIFF, one could install a TIFF to GIF converter. Other useful filters are, e.g., plain text to HTML, and HTML to Postscript. Printer drivers are like viewers, except that they output to a printer and not to the screen. The success of the W3A approach depends on wide enough acceptance. It is designed with the dual goal of being easy to implement and easy to install by end-users.