Add Depth of Retrieval Clause

An example of this representation can be found in annex C, clause C.2.2.1.3.

### 7.7.4 Depth of retrieval

When retrieving [Linked Entities]{.HTML-Keyboard}, the [Linking

Entity]{.HTML-Keyboard} may have a _Relationships_ to [Linked

Entities]{.HTML-Keyboard} which may in turn have a _Relationships_, to further

[Linked Entities]{.HTML-Keyboard}. Complete traversal of a densely or

recursively linked Entity graph would result in payloads of an excessive length.

Therefore to mitigate this, the default depth of retrieval (or _`joinLevel_)

shall be set to one, though this may be overridden on request. Furthermore,

whenever a [Linked Entity]{.HTML-Keyboard} has already been encountered during

graph traversal, its [Linked Entities]{.HTML-Keyboard} shall not undergo further

expansion.

## 7.8 Tenants

#### 7.8.1 Introduction