EditX := 10, EditY := 10, EditW := 600, EditH := 400

Gui, +hwndhParent

Gui, Child:Default
Gui, -Caption +ToolWindow +Parent%hParent%
Gui, Add, Edit, hwndhEdit x0 y0 w%EditW% h%EditH%

VarSetCapacity(WINDOWINFO, 60, 0)
DllCall("GetWindowInfo", Ptr, hEdit, Ptr, &WINDOWINFO)
editClientX := NumGet(WINDOWINFO, 20, "Int")
editWindowX := NumGet(WINDOWINFO, 4, "Int")
editBorderWidth := editClientX - editWindowX

GuiControl, Move, %hEdit%, % "x" -editBorderWidth " y" -editBorderWidth
                          . " w" EditW + editBorderWidth*2 " h" EditH + editBorderWidth*2

Gui, Show, x%EditX% y%EditY% w%EditW% h%EditH%
Gui, %hParent%: Show, % "w" EditW + 20 " h" EditH + 20
Return

GuiClose:
   ExitApp