Very important feature, been missing it since forever, one of the first things i noticed missing when beginning with Blender. Triples the workflow efficiency.

@William Reynish (billreynish) If you have 5 minutes to spare, read the PDF i attached, a page and a half in length. It is a small comment i gave to the author of the Blender Archipack addon, regarding possible multi - element property editing capabilities. I described the multi element property panel in CAD apps which i know and work with on daily basis. If you get a copy of QCAD application (GPL licensed) on one of your machines, you can see the it in action. The pdf describes the basic logic behind it, perhaps you can use in for inspiration. CAD apps are the best at this, no doubt.

Basic introduction of the panel, not showing the best feature - dealing with multi category element selection. Speed up x 2 - the video is slow.
https://www.youtube.com/watch?v=VHLqtZ3bGgo

P.S. - What i mean you could try to expand multi element editing to whole property editor. Show only tabs (object / mesh / modifiers...) that are common for selection and on them only common values, according to selection. A selection filter drop down on the top for expanding the list of editable values - check the PDF...

P.S.P.S. - Industry standard for relative marker is @. Perhaps you can find some similar marker, because in my keyboard layout i can't find the 'double S' symbol. Perhaps you could try & or # or sth like that...

Okavango: We cannot do it that way. It would be very very slow, because Blender then has to constantly compare values. If you select 1.000 objects, Blender then needs to check the the values on all those objects and continually compare them. That's likely to be hundreds of thousands of values compared constantly.

The design outlined at the top works around that issue, and can be fast, because it doesn't have to compare hundreds of values for every single object selected.

Ah ok.
I trust you on this, i don't know the technical side of the implementation.

:) We may adopt @ though - we already discussed that as a possibility too.

Cool :) Check the intellectual property though. Some big companies use it, although i think some open source do also. Check LibreCAD, QCAD, i believe it is safe.

Not sure if this fits entirely in this task, but since there seem to be changes in the way input values are treated, Would it be very hard to support ignoring leading zeroes?
Currently if one accidentally types 05 or 003 in a value box it fails to set the property, and the input is ignored and reset to previous value.

Huh, that would be good to fix, yes. Dalai already fixed the issue where if you pressed backspace to delete the value, nothing would happen. Now it resets the value.

Maybe the selected value could be a little less than white, so a white box would be visible around the value, when the value is only added to the active element.

Nb. using the orange color for entire selection, would have to be consistent throughout Blender including the Sequencer, which currently doesn't use outline for selection.