[*] General code improvement.

* Rework navigation allowing direct management and triggering for grabkeyboard widgets.
* Navigation code now behaves better with deeply nested layouts.
* Allow widget hierarchies deeper than 2 (__call() is implemented for every Widget metatable).
* Make BASE locals more secure (match '<filename>$' in regexp)

widget.lua

@@ -1,9 +1,7 @@
 local rectunion = require('lib.gear.rect').union
 
 local Widget = {
-    __call = function(cls, args)
-        return cls.new(args)
-    end
+    __call = function(cls, args) return cls.new(args) end
 }
 Widget.__index = Widget
 
@@ -40,25 +38,26 @@ function Widget:grabFocus()
     if focused ~= nil then
         -- Notify leave
         focused.hovered = false
-        if focused.grabkeyboard then
-            if love.system.getOS() == 'Android' or love.system.getOS() == 'iOS' then
-                love.keyboard.setTextInput(false)
-            end
-            love.keyboard.setKeyRepeat(false)
-        end
-
+        -- Widget specific focus loss
+        focused:loseFocus()
+        -- Event handler
         focused:onLeave()
+
+        if focused.grabkeyboard then
+            -- If focused widget stole input,
+            -- then drop current input snapshot, since
+            -- those events should have been already
+            -- managed directly
+            ui.device:snapshot()
+        end
     end
 
     local wasHovered = self.hovered
 
     self.hovered = true
-    if self.grabkeyboard then
-        love.keyboard.setTextInput(true, self.x,self.y,self.w,self.h)
-        love.keyboard.setKeyRepeat(true)
-    end
     if not wasHovered then
         -- First time hovered, notify enter
+        self:gainFocus()
         self:onEnter()
     end
 
@@ -100,7 +99,11 @@ function Widget:colorForState()
     end
 end
 
--- Common NOP event handlers
+-- NOP hooks for UI internal use
+function Widget:loseFocus() end
+function Widget:gainFocus() end
+
+-- NOP event handlers, publicly overridable
 function Widget:onHit() end
 function Widget:onEnter() end
 function Widget:onLeave() end