[EscherechiaColi]

I totally messed up sorry! Of course, here is the correct .xml file:

<GuiXml>
  <Controls>
    <TopLevelControl name="RemiCustomAddonIndicator" mouseEnabled="true" movable="true" clampedToScreen="true">
      <Dimensions x="200" y="25" />
      <Anchor point="BOTTOM" relativeTo="GuiRoot" relativePoint="CENTER" offsetY="-20" />
      <OnInitialized>
          -- LUA code here. This is where you'd check to see if the control needs to be hidden or not.
          RemiCustomAddonIndicator:SetHidden(not (GetNumBagFreeSlots(1) < 10))
      </OnInitialized>
      <OnMoveStop>
        RemiCustomAddon.OnIndicatorMoveStopBagSpace()
      </OnMoveStop>

      <Controls>
        <Label name="$(parent)Label" width="200" height="25" font="ZoFontWinH1" inheritAlpha="true" color="FFA500"
            wrapMode="TRUNCATE" verticalAlignment="TOP" horizontalAlignment="CENTER" text="Your bag is almost full!">
          <Anchor point="TOP" relativeTo="$(parent)" relativePoint="TOP" />
        </Label>
      </Controls>
    </TopLevelControl>
  </Controls>
</GuiXml>

Thank you for your answers so far!