This layer's sole purpose is simple! It sets one variable, BBLAYERS_LAYERINDEX_URL, and is sets it to "https://layers.zeptoinitiative.org/layerindex/", i.e. BBLAYERS_LAYERINDEX_URL = "https://layers.zeptoinitiative.org/layerindex/" And it does that in order to make use of the Zepto layerindex.