Add info about CNAME flatenning to iDNS docs

Author: RebeccaTamachiro

src/content/docs/dns/cname-flattening/index.mdx

@@ -6,16 +6,12 @@ sidebar:
   label: About
 ---
 
-import { Render } from "~/components"
+import { Render, GlossaryTooltip } from "~/components"
 
-CNAME flattening speeds up CNAME resolution and allows you to use a CNAME record at your root/apex domain (`example.com`).
+CNAME flattening speeds up CNAME resolution and allows you to use a CNAME record at your <GlossaryTooltip term="zone apex" link="/dns/concepts/#zone-apex">zone apex</GlossaryTooltip> (`example.com`).
 
 :::note
-
-
 This functionality is also what allows you to use a [root custom domain](/pages/configuration/custom-domains/) with a Cloudflare Pages site.
-
-
 :::
 
 ## How it works

src/content/docs/dns/internal-dns/internal-zones/index.mdx

@@ -29,4 +29,15 @@ Internal zones can contain the same [DNS record types](/dns/manage-dns-records/r
 
 You can manage internal DNS records in the same way as you would manage public DNS records, with the difference that [proxy status](/dns/proxy-status/) does not apply to internal DNS records.
 
-Refer to [Manage DNS records](/dns/manage-dns-records/how-to/create-dns-records/) or to the [API documentation](/api/resources/dns/subresources/records/) for further guidance.
+Refer to [Manage DNS records](/dns/manage-dns-records/how-to/create-dns-records/) or to the [API documentation](/api/resources/dns/subresources/records/) for further guidance.
+
+### CNAME flattening
+
+With CNAME flattening, Cloudflare finds the IP address that a CNAME points to and then returns the final IP address instead of a CNAME record. With Internal DNS, this behavior is applied by default and cannot be turned off.
+
+Cloudflare will try to flatten the CNAME record within the same [DNS view](/dns/internal-dns/dns-views/). If that is not possible, the following will happen:
+
+1. The CNAME record is returned to Gateway resolver as-is.
+2. Gateway resolver will process the returned record, depending on the **Fallback through public DNS** configuration:
+    - On: Gateway will try to resolve the query by sending it to Cloudflare's public DNS resolver ([1.1.1.1](/1.1.1.1/)).
+    - Off: Gateway will return the response as-is to the client.

src/content/glossary/dns.yaml

@@ -79,3 +79,7 @@ entries:
       When a [DNS record is proxied](/dns/proxy-status/), requests are processed according to your configurations, and Cloudflare can optimize, cache, and protect your domain. Refer to [How Cloudflare works](/fundamentals/concepts/how-cloudflare-works/) for details.
     associated_products:
       - Fundamentals
+
+  - term: zone apex
+    general_definition: |-
+      zone apex refers to the domain or subdomain on which the control of DNS records starts.