[DNS] Add $ORIGIN, $TTL and $GENERATE directive support for zone file (#16120)

* [DNS] Add $ORIGIN, $TTL and $GENERATE directive support for zone file

Add DNS Zone File Directives support

* Add the error context, $INCLUDE directive not allowed

* Text review: paragraphs re-org and style guide adjustments

* Add link to BIND docs on  directive

---------

Co-authored-by: Rebecca Tamachiro <[email protected]>

Author: 2 people

src/content/docs/dns/manage-dns-records/how-to/import-and-export.mdx

@@ -12,10 +12,7 @@ Use import and export to have more control over your DNS records and make proces
 ## Import records
 
 :::caution
-
-{" "}
-
-<Render file="zone-file-size-limit" />
+ <Render file="zone-file-size-limit" />
 :::
 
 ### Format your zone file
@@ -92,3 +89,11 @@ f.example.com.  60  IN  A   1.1.1.1 ; this is the comment cf_tags=tag1:value1,ta
 ; Neither attribute
 g.example.com.  60  IN  A   1.1.1.1
 ```
+
+## DNS zone file directives
+
+A DNS zone file can be constructed using directives in addition to resource records (RRs). Directives start with `$` and are standardized - `$ORIGIN` and `$INCLUDE` are defined in [RFC 1035](https://www.rfc-editor.org/rfc/rfc1035#section-5.1), and `$TTL` is defined in [RFC 2308](https://www.rfc-editor.org/rfc/rfc2308). Additionally, BIND provides the [non-standard](https://bind9.readthedocs.io/en/latest/chapter3.html#bind-primary-file-extension-the-generate-directive) `$GENERATE` directive.
+
+Cloudflare supports `$ORIGIN`, `$TTL`, and `$GENERATE` directives.
+
+`$INCLUDE` is not supported. When a zone file contains a `$INCLUDE` directive, Cloudflare responds with a parsing error `$INCLUDE directive not allowed`.