A resource can map to the empty set, which allowsreferences to be made to a concept before any realization ofthat concept exist

Should the W3C be disbanded, then any Web site will be granted the right to make a copy (at a different URI) of all public persistent resources so long as they are not modified and are preserved in their entirety and made available free of charge, and provided the same persistence policy is applied to these "historical mirrors." In such event, the original https://www.w3.org web site will be handed over for management to another organization only if that organization pledges to this policy or one considered more persistent.