/usr/share/GNUstep/Documentation/Developer/netclasses/ is in libnetclasses-dev 1.06.dfsg-5build3.
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/usr/share/GNUstep/Documentation/Developer/netclasses/LineObject.gsdoc
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/usr/share/GNUstep/Documentation/Developer/netclasses/netclasses.igsdoc
/usr/share/GNUstep/Documentation/Developer/netclasses/overview.html
/usr/share/GNUstep/Documentation/Developer/netclasses/synchronous.html