Unless you're really in love with XML from some prior programming experience, I'd suggest writing your addon in Lua only. It's much less verbose, and reduces the need for you to learn two separate syntaxes:
Code:
local frame = CreateFrame("Frame", "barAWindow", UIParent)
frame:SetSize(1800, 300)
frame:SetPoint("CENTER")
frame:SetAlpha(0.8)
local bg = frame:CreateTexture(nil, "BACKGROUND")
bg:SetAllPoints(true)
bg:SetTexture("Interface\\AddOns\\ZBar\\ZBarImgs\\barA")
frame:SetMovable(true)
frame:SetScript("OnMouseDown", frame.StartMoving)
frame:SetScript("OnMouseUp", frame.StopMovingOrSizing)