Provides layout modifier UseTransientFor: when a float has focus and is WM_TRANSIENT_FOR a tile, run the underlying layout as if that tile had focus.

Apply to your layout in a config like:

main = xmonad (def{
                  layoutHook = trackFloating (useTransientFor
                      (noBorders Full ||| Tall 1 0.3 0.5)),
                  ...
              })

useTransientFor and trackFloating can be enabled independently. For example when the floating window sets WM_TRANSIENT_FOR, such as libreoffice's file->preferences window, optionA will have the last-focused window magnified while optionB will result magnify the window that opened the preferences window regardless of which tiled window was focused before.

import XMonad.Layout.Magnifier
import XMonad.Layout.TrackFloating

underlyingLayout = magnifier (Tall 1 0.3 0.5)

optionA = trackFloating underlyingLayout
optionB = trackFloating (useTransientFor underlyingLayout)

It also corrects focus issues for full-like layouts inside other layout modifiers:

import XMonad.Layout.IM
import XMonad.Layout.Tabbed
import XMonad.Layout.TrackFloating
import XMonad.Layout.Reflect

gimpLayout = withIM 0.11 (Role "gimp-toolbox") $ reflectHoriz
      $ withIM 0.15 (Role "gimp-dock") (trackFloating simpleTabbed)

Interactions with some layout modifiers (ex. decorations, minimizing) are unknown but likely unpleasant.