[mulesh]

I think this will work, havent play-tested it, but I have a good feeling

XML file:

<Ui xmlns="http://www.blizzard.com/wow/ui/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.blizzard.com/wow/ui/
..\FrameXML\UI.xsd">

<Script file="FocusEye.lua"/>

<Button name="FocusButton" parent="UIParent" toplevel="true" hidden="false" enableMouse="true" movable="true" inherits="SecureActionButtonTemplate">
  <Layers>
    <Layer level="ARTWORK">
      <Texture name="MyTexture" file="Interface\AddOns\FocusEye\Clear"/>
    </Layer>
  </Layers>
  <Size>
    <AbsDimension x="20" y="20"/>
  </Size>
  <Anchors>
    <Anchor point="TOPRIGHT"/>
      <Offset>
        <AbsDimension x="-200" y="-200"/>
      </Offset>
    </Anchor>
  </Anchors>

  <Scripts>
    <OnLoad>this:RegisterForDrag("LeftButton"); thisRegisterForClicks("LeftButtonUp");
    <OnClick>FocusToggle();</OnClick>
    <OnDragStart>this:StartMoving();</OnDragStart>
    <OnDragStop>this:StopMovingOrSizing();</OnDragStop>
    <OnEnter>FocusEnter();</OnEnter>
    <OnLeave>FocusLeave();</OnLeave>
  </Scripts>

</Button>
</Ui>

LUA file:

function FocusToggle()
  if UnitExists("focus") then
    FocusUnit("none");
    FocusButton:SetTexute(Interface\AddOns\FocusEye\Clear);
  elseif UnitExists("target") then
    FocusUnit("target");
    FocusButton:SetTexture(Interface\AddOns\FocusEye\Focussed);
  end
end

function FocusEnter()
  GameTooltip:SetOwner(this, "ANCHOR_RIGHT");
  GameTooltip:SetText("Focus\nLeft-Click to set focus");
  GameTooltip:Show();
end

function FocusLeave()
  GameTooltip:Hide();
end

I added some tooltip code and some script events for dragging.

Good luck!