gistfile1.txt

    local create = function(plate)
        plate.target = plate:CreateTexture(nil, 'OVERLAY')
        plate.target:SetWidth(30) plate.target:SetHeight(30)
        plate.target:SetPoint('BOTTOMLEFT', plate, 'TOPLEFT')
        plate.target:SetTexture[[Interface\Tooltips\UI-Tooltip-Background]]
        plate.target:SetVertexColor(1, 0, 0)
        plate.target:Hide()
        plate.modded = true
    end

    local isPlate = function(frame)
        local overlayRegion = frame:GetRegions()
        if not overlayRegion or overlayRegion:GetObjectType() ~= 'Texture'
        or overlayRegion:GetTexture() ~= [[Interface\Tooltips\Nameplate-Border]] then
            return false
        end
        return true
    end

    local matchPlate = function(plate)
        if plate.target then
            local health = plate:GetChildren()
            local _, _, name = plate:GetRegions()
            local text   = name:GetText()
            local target = GetUnitName'target'
            if target == text and health:GetAlpha() == 1 then plate.target:Show() else plate.target:Hide() end
        end
    end

    local f = CreateFrame'Frame'
    f:SetScript('OnUpdate', function()
        local frames = {WorldFrame:GetChildren()}
	    for _, plate in ipairs(frames) do
            if isPlate(plate) and plate:IsVisible() then
                if not plate.modded then create(plate) end
                matchPlate(plate)
            end
        end
    end)

    --