Link to specification

Author: ralfhandl

registries/_namespace/oai.md

@@ -6,7 +6,7 @@ layout: default
 ---
 
 {% capture summary %}
-The `x-{{page.slug}}-` prefix is reserved for uses defined by the [OpenAPI Initiative](https://www.openapis.org/).
+The `x-{{page.slug}}-` prefix is [reserved](https://spec.openapis.org/oas/v3.1.0.html#specification-extensions) for uses defined by the [OpenAPI Initiative](https://www.openapis.org/).
 {% endcapture %}
 
 {% include namespace-entry.md summary=summary %}

registries/_namespace/oas.md

@@ -6,7 +6,7 @@ layout: default
 ---
 
 {% capture summary %}
-The `x-{{page.slug}}-` prefix is reserved for uses defined by the [OpenAPI Initiative](https://www.openapis.org/).
+The `x-{{page.slug}}-` prefix is [reserved](https://spec.openapis.org/oas/v3.1.0.html#specification-extensions) for uses defined by the [OpenAPI Initiative](https://www.openapis.org/).
 {% endcapture %}
 
 {% include namespace-entry.md summary=summary %}