Description: this code adds a new output filter to dot/tcldot. The new filter is called "imap". It is used just like "ps," "ismap," "gif," and the rest of the output filters. The new filter produces an "imap" file, the new-style Apache-compatible equivalent of the old-style "ismap" file which dot already knows how to produce. In either case, the purpose is to map regions or points on a gif image to URLs, so that the user of a web browser can click on the gif image and activate anchors that invoke other pages. The "ismap" map file style which was commonly used with early (NCSA) http servers required an external mapping mechanism kept in the cgi-bin dir (ismap executable or user-supplied equivalent), whereas recent Apache servers include the imap functionality in the server itself. To configure an Apache server to use imap files correctly, uncomment this line # If you wish to use server-parsed imagemap files, use AddHandler imap-file map in srm.conf. From then on, you can use files of the form mumble.map as follows: The .map file will be used as the image map for the associated gif image. The new "imapgen" filter for dot produces valid imap files for use with Apache servers. In addition to being Apache-compliant, the imap file produced by imapgen can include clickable edge points as well as node rectangles. If the attribute "URL" is defined for an edge, then the label virtual node will be bound/mapped to that URL, as will spline points along the edge. If the special attributes "tailURL" and/or "headURL" are set, then the head and tail points of the edge will be bound to those URL, otherwise the head and tail will default to the main URL. The older ismapgen code did not support edge URLs. [JCE may wish to correct my wording in the description of ismap (old-style) files above]