Pointer to code re how it does the below please?

[callagga]

Hi just trying to get my head around the codebase & would appreciate just a couple of quick pointers to the code regarding how it does:

(A) Whilst dragging it shows what the end result would look like when it crosses a valid drop point?

(B) How does it do animated moves of background rectangles as these do move during a drag (per item A above) to show possible future state

Perhaps where in code base/how this is done, or whether is this performed by one of the imported libraries?