inkjar is a USE flag used by inkscape package. Let's see it's description: $ fgrep inkjar use.local.desc media-gfx/inkscape:inkjar - enables inkjar support Well, inkjar enables... inkjar support! Not very descriptive. Unfortunately, neither the web nor the README file appears to know what's inkjar. Finally, I could find what it is by looking at ./configure --help output: --without-inkjar disable openoffice files (SVG jars) So, I suggest that this USE flag description be changed to something similar to the ./configure --help. After all, USE flag descriptions exist to make the life easier for the users.
media-gfx/inkscape:inkjar - enables support for OpenOffice.org SVG jar files