While spelunking in the xclip source code, I noticed it had much the same call to createSimpleWindow but with a simpler geometry - just 1x1 pixels, not the odd 200x100 of the original code. It seems to work the same and looks better and less mysterious, so unless arossato had a specific reason for those particular two numbers...
This is based on Andrea Rossato's standalone tools and is meant for integration straight into a Config.hs. It offers two main functions, 'getSelection' and 'putSelection', whose names should be self-explanatory.