Help with PetFrame 'pet experience bar'

[Inokis]

I'm trying to add a pet experience bar to my PetFrame xml, however so far I can only get it to display after visiting the Stable Master. I'm not sure what i'm doing wrong but perhaps someone can help me out here:

LUA:

function PetFrame_OnLoad()
      this:RegisterEvent("UNIT_PET_EXPERIENCE");
      PetFrameExpBar_Update();
end

function PetFrame_Update()
      PetFrameExpBar_Update();
end

function PetFrame_OnEvent(event)
      UnitFrame_OnEvent(event);
      	if ( event == "UNIT_PET_EXPERIENCE" ) then
		PetFrameExpBar_Update();
	end
end

function PetFrameExpBar_Update()
	local currXP, nextXP = GetPetExperience();
	PetFrameExpBar:SetMinMaxValues(min(0, currXP), nextXP);
	PetFrameExpBar:SetValue(currXP);
end

XML:

<StatusBar name="PetFrameExpBar" inherits="TextStatusBar">
     <Size>
	<AbsDimension x="122" y="3"/>
     </Size>
	<Anchors>
   	     <Anchor point="TOPLEFT">
		<Offset>
			<AbsDimension x="-5" y="-18"/>
		</Offset>
	    </Anchor>
	</Anchors>
	<Scripts>
		<OnLoad>
			PetFrameExpBar_Update();
			TextStatusBar_Initialize();
			this:Show();
		</OnLoad>
		<OnEvent>
			PetFrameExpBar_Update();
		</OnEvent>
	</Scripts>
	<BarTexture file="Interface\TargetingFrame\UI-StatusBar"/>
		<BarColor r="1.0" g=".32" b="1.0"/>
</StatusBar>

[Inokis]

I finally got it to work:

this:RegisterEvent("PET_BAR_UPDATE");