In various places (e.g. quantiy claims with units 1) we refer to items via their entity urls such as http://www.wikidata.org/entity/Q712226.
Yet there is no easy way of determining what the stem/prefix (i.e. http://www.wikidata.org/entity/ for wikidata) is for a given wikibase installation. Hence it would be useful if this could be included in the siteinfo api call (cf. articlepath).
Note that just /entity/ isn't enough (unlike for articlepath) here since the protocol is http rather than the site default which is https.