docs(spec): indicate in detail how Channel Item Object field resolves

Refs asyncapi#612

spec/asyncapi.md

@@ -565,7 +565,7 @@ Describes the operations available on a single channel.
 
 Field Name | Type | Description
 ---|:---:|---
-<a name="channelItemObjectRef"></a>$ref | `string` | Allows for an external definition of this channel item. The referenced structure MUST be in the format of a [Channel Item Object](#channelItemObject). If there are conflicts between the referenced definition and this Channel Item's definition, the behavior is *undefined*. <br/><br/>**Deprecated:** Usage of the `$ref` property has been deprecated.
+<a name="channelItemObjectRef"></a>$ref | `string` | Allows for an internal or external definition of this channel item. The referenced structure MUST be in the format of a [Channel Item Object](#channelItemObject). If there are conflicts between the referenced definition and this Channel Item's definition, the behavior is *undefined*. Rules of resolving are defined by [JSON Reference](https://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03) specification. <br/><br/>**Deprecated:** Usage of the `$ref` property has been deprecated.
 <a name="channelItemObjectDescription"></a>description | `string` | An optional description of this channel item. [CommonMark syntax](https://spec.commonmark.org/) can be used for rich text representation.
 <a name="channelItemObjectServers"></a>servers | [`string`] | The servers on which this channel is available, specified as an optional unordered list of names (string keys) of [Server Objects](#serverObject) defined in the [Servers Object](#serversObject) (a map). If `servers` is absent or empty then this channel must be available on all servers defined in the [Servers Object](#serversObject).
 <a name="channelItemObjectSubscribe"></a>subscribe | [Operation Object](#operationObject) | A definition of the SUBSCRIBE operation, which defines the messages produced by the application and sent to the channel.