* more handy in certain cases (more facilities without usage of keyboard)
* wheel often functions as middle mouse button, so that a combination middle+wheel to scroll f.i. horizontally will be especially meaningful
* possibly more functions to be selected in the future for additional modifierkeyless combinations (f.e. Wish 154707)

Thank you for the feature suggestion and sorry for the long time without an answer.

Pressing two mouse buttons at exactly the same time is not easy. Everybody who tried to use left+right=middle will know that :-) Furthermore on many input devices it is not possible to perform several button clicks at the same time.

Given these constraints from the input devices I doubt it makes any sense to extend this functionality.

To me it would be a killer-feature as having to use the alt or meta key of the keyboard to move or resize windows can be very unhandy (missing the keyboard because my hand is on the mouse). Why not simply let the middle mouse button be used as Alt- or Meta key?

> To me it would be a killer-feature as having to use the alt or meta key of
> the keyboard to move or resize windows can be very unhandy (missing the
> keyboard because my hand is on the mouse). Why not simply let the middle
> mouse button be used as Alt- or Meta key?
Middle mouse button has already a very specific meaning on X11, we don't want 
to conflict with that.

Furthermore you can of course just map the mouse button to the modifier key if 
that helps you.

Well; using xmodmap would be a good idea. However I neither wanna map the Alt nor the Window key because both are in use for other valuable key combinations at me. Why not offer a third virtual xmodmappable key for window operations like resizing and moving windows?

> Well; using xmodmap would be a good idea. However I neither wanna map the
> Alt nor the Window key because both are in use for other valuable key
> combinations at me. Why not offer a third virtual xmodmappable key for
> window operations like resizing and moving windows?
The number of modifier keys is rather limited. We provide the choice between 
two. The third available modifier key is in general taken by applications, 
e.g. ctrl+left click a link in any browser. It does not make any sense to add 
another meta key.

I'm sorry that we cannot help here. Please understand that implementing each 
feature request is not possible. I consider this feature already good enough 
and there are enough possibilities to get what you want.

No. If you have ever used this feature then window moving can be achieved by Alt+Left mouse button and Alt+Right mouse button. Alt can be changed to the meta key instead; however I would need a "virtual" key instead of the meta key which is already in use.

afaik xmodmap offers a lot of meta key up to a 5th and 6th.

not only would it be new to me that xmodmap could map between mouse buttons and keys*, but also latter mentioned "modifiers" are likely nth level selectors (altgr)
available modifiers are alt, shift, ctrl & meta - only alt & meta are not in regular application use (iirc gimp even uses alt fo a selection mode)

using parallel clicks not only requires a skilled user, but would also horribly mess up the kwin eventhandler, cause delayed mouse input in *every* window, force us to keep a passive grab on each client (ie also the active one, what will at least break legacy applications) and pot. conflict with the x11 3-button emu (kludge itself)

-> with qt5 we should gain handling of > 3 buttons (+the wheel, oc) so if your mouse has extra buttons, you could use one of them - in fact you already can, because
*xbindkeys should be able to do so
and it also allows to program a mouse button to perform alt+lmb