Add error condition

  shall give back metadata about the _`@context`_ that corresponds to the

  indicated local identifier. It shall give back [ResourceNotFound]{.HTML-Error}

  error if the identifier is not found.

- if [core]{.HTML-Variable} is present, the broker shall return an _`@context`_

  in the form of an array of reference URLs (as defined in the JSON-LD

  specification [n.8] section 3.1). The array shall hold two items - one URL

  reference for the original location of the requested user _`@context`_, and

  one URL for the location of the core _`@context`_.

- if [core]{.HTML-Variable} is present, and it does not conform to a

  semantically versioned string, a [BadRequest]{.HTML-Error} error shall be

  returned.

- if [core]{.HTML-Variable} is present and it conforms to a semantically

  versioned string, the broker shall return an _`@context`_ in the form of an

  array of reference URLs (as defined in the JSON-LD specification [n.8] section

  3.1). The array shall hold two items - one URL reference for the original

  location of the requested user _`@context`_, and one URL for the location of

  the core _`@context`_.

- Otherwise, if [details]{.HTML-Variable} is set to [false]{.HTML-Variable}, or

  [details]{.HTML-Variable} is not present, the broker shall give back the full

  content of the _`@context`_ that corresponds to the indicated local