Clarify entry/complete document terminology (3.1.1)

Clarifies that there can be multiple complete OpenAPI documents,
only one of which is an entry OpenAPI document.

Author: handrews

versions/3.1.1.md

@@ -149,7 +149,10 @@ In order to preserve the ability to round-trip between YAML and JSON formats, YA
 
 ### <a name="documentStructure"></a>OpenAPI Description Structure
 
-An OpenAPI Description (OAD) MAY be made up of a single document or be divided into multiple, connected parts at the discretion of the author. In the latter case, [Reference Object](#referenceObject), [Path Item Object](#pathItemObject) and [Schema Object](#schemaObject) `$ref` keywords, as well as the [Link Object](#linkObject) `operationRef` keyword, are used.  In a multi-document description, the document containing the [OpenAPI Object](#oasObject) is known as the **entry OpenAPI document.**
+An OpenAPI Description (OAD) MAY be made up of a single document or be divided into multiple, connected parts at the discretion of the author. In the latter case, [Reference Object](#referenceObject), [Path Item Object](#pathItemObject) and [Schema Object](#schemaObject) `$ref` keywords, as well as the [Link Object](#linkObject) `operationRef` keyword, are used.
+
+Any document consisting entirely of an OpenAPI Object is known as a **complete OpenAPI document**.
+In a multi-document description, the document containing the [OpenAPI Object](#oasObject) where parsing begins for a specific API's description is known as that API's **entry OpenAPI document**, or simply **entry document**.
 
 It is RECOMMENDED that the entry OpenAPI document be named: `openapi.json` or `openapi.yaml`.