In Blender 2.8, we want to make it easier to set values for multiple objects or bones at once. In version 2,79 you can do this, but you have to right-click on a value after you've changed it at pick Copy to Selected from the menu. This is both slow and unnecesary.
Instead we want to make it so you can simply type a value, hit return, and that value then automatically gets propagated to all the relevant objects or bones.
//Note: For technical reasons, we cannot make this work for nodes, because it's not easy to figure out how to find the correct pair mapping. So we need a way for the user to know which items can work and which items cannot. We also cannot do real-time compares of 3000 selected objects to display special indicators if values are the same or they differ. So we have to work around these limitations.//
This is how we've decided to solve this:
If the user has more than one object or bone selected, and then goes to edit a value, we display a 'selected' outline around the property, to indicate that this will affect all selected items. The user simply types a value and hints return.
Additionally, we want to make it easy to type in // relative // values too. We allow this by using =, so the user can type '= -3' to subtract 3 from the value on all selected objects or bones, like so:
To edit the value of only the active item, even if multiple ones are selected, we can invert the Alt-key behaviour, so holding Alt will only edit the value on the active item.