All safe methods are also idempotent, but not all idempotent methods are safe. For example, PUT and DELETE are both idempotent but unsafe.

Holocaust denial is a subset of genocide denial, which is a form of politically motivated denialism.

An Euler diagram (/ˈɔɪlər/, OY-lər) is a diagrammatic means of representing sets and their relationships. They are particularly useful for explaining complex hierarchies and overlapping definitions. They are similar to another set diagramming technique, Venn diagrams. Unlike Venn diagrams, which show all possible relations between different sets, the Euler diagram shows only relevant relationships.

Every URL is a URI; Every URN is a URI; URI and URL are NOT interchangeable – a URL is a URI, but a URI is not always a URL; URLs always contain an access mechanism.

Escaping is a subset of encoding, where not all characters need to be encoded. Only some characters are encoded (by using an escape character).

Note that the point of JSON-LD is that it's just JSON, in this case using the schema.org context to interpret the values.