After reading the windows rules wiki of kwin and trying a few things in the debian/jessie kde installation I'm not sure I can accomplish the following fluxbox feature I'm quite a big fan of: #298 percentage values in apps file

This feature does allow you to set percentage geometry values for window size & position with respect to your display resolution. An example: 50%:100% geometry will allow an app window to always cover half of the desktop regardless of screen resolution. This is why it's so much easier to move a user profile to a different machine (pc -> laptop). If you set window rules in absolute values instead of percentage, the windows will be placed badly on the smaller screen, you will have to readjust the absolute values.

Maximizing horizontally/vertically can be done in kwin/kde already, what about setting size to 50% screen coverage? You could use half of the screen more easily without the need to use drag and drop and windows snapping?

A penny for your thoughts on that feature?

https://bugs.kde.org/show_bug.cgi?id=314388
https://bugs.kde.org/show_bug.cgi?id=132347

Could be done for KDE5 -> [0,1] implies percentage (requires int -> float) and egative values right/bottom alignment.

You /can/ right now write a script to programatically control window sizes, but extending the rule capability may be a low hanging fruit.

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'cause of inflation I want a shilling (now 5 pence, then worth 12)