Describe the project you are working on:
Not related to any project.
Describe the problem or limitation you are having in your project:
When assigning a texture to e.g. a button, the textures are folded behind a Textures section. If you are dragging a texture before unfolding it, you must drop it, unfold and then do it again. This is also true for dragging nodes or other resources.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
When dragging a file or node over an inspector section, it opens up and allows the the underlying fields to be assigned.
Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
I have made an early version showing how it would work:

It could be expanded by not instantly opening up a section, but waiting for a certain duration. Other suggestions are welcome.
If this enhancement will not be used often, can it be worked around with a few lines of script?:
I'm not sure if this could be easily scripted, but I imagine this feature will be used quite often regardless.
Is there a reason why this should be core and not an add-on in the asset library?:
Basic usability feature
I think it should just unfold after holding something on it for a while (half a second or so). If it would expand directly, when you drag something over it, you'd have very much unfold sections and then it's work-intensive to fold them again. Oh yes, you already wrote that. Nevertheless here's someone who wants it only if this is the case 馃槃
With this change it becomes a little more complex. When waiting you also need to give feedback that you are hovering over it.

Yes, it needs a little bit of delay, not half a second, but at least 0.1 or 0.2 seconds. Otherwise, if you hover over the inspector vertically, you're going to expand everything which would be very annoying.
In the gif above the delay is set at 1 second, because 0.5 already felt a little too quick.
I think 1 second is far too long. The point is only to avoid doing something the user does not expect, but it should still stay a little bit more responsive.
Anyway, that can be tuned later on. :)
Most helpful comment
I think it should just unfold after holding something on it for a while (half a second or so). If it would expand directly, when you drag something over it, you'd have very much unfold sections and then it's work-intensive to fold them again. Oh yes, you already wrote that. Nevertheless here's someone who wants it only if this is the case 馃槃