# D\_EXTEND

`D_EXTEND` adds records (and metadata) to a domain previously defined by [`D()`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d.md). It can also be used to add subdomain records (and metadata) to a previously defined domain.

The first argument is a domain name. If it exactly matches a previously defined domain, `D_EXTEND()` behaves the same as [`D()`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d.md), simply adding records as if they had been specified in the original [`D()`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d.md).

If the domain name does not match an existing domain, but could be a (non-delegated) subdomain of an existing domain, the new records (and metadata) are added with the subdomain part appended to all record names (labels), and targets (as appropriate). See the examples below.

Matching the domain name to previously-defined domains is done using a `longest match` algorithm. If `domain.tld` and `sub.domain.tld` are defined as separate domains via separate [`D()`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d.md) statements, then `D_EXTEND("sub.sub.domain.tld", ...)` would match `sub.domain.tld`, not `domain.tld`.

Some operators only act on an apex domain (e.g. [`CF_SINGLE_REDIRECT`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/domain-modifiers/service-provider-specific/cloudflare-dns/cf_single_redirect.md), [`CF_REDIRECT`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/domain-modifiers/service-provider-specific/cloudflare-dns/cf_redirect.md), and [`CF_TEMP_REDIRECT`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/domain-modifiers/service-provider-specific/cloudflare-dns/cf_temp_redirect.md)). Using them in a `D_EXTEND` subdomain may not be what you expect.

{% code title="dnsconfig.js" %}

```javascript
D("domain.tld", REG_MY_PROVIDER, DnsProvider(DNS),
  A("@", "127.0.0.1"), // domain.tld
  A("www", "127.0.0.2"), // www.domain.tld
  CNAME("a", "b"), // a.domain.tld -> b.domain.tld
);
D_EXTEND("domain.tld",
  A("aaa", "127.0.0.3"), // aaa.domain.tld
  CNAME("c", "d"), // c.domain.tld -> d.domain.tld
);
D_EXTEND("sub.domain.tld",
  A("bbb", "127.0.0.4"), // bbb.sub.domain.tld
  A("ccc", "127.0.0.5"), // ccc.sub.domain.tld
  CNAME("e", "f"), // e.sub.domain.tld -> f.sub.domain.tld
);
D_EXTEND("sub.sub.domain.tld",
  A("ddd", "127.0.0.6"), // ddd.sub.sub.domain.tld
  CNAME("g", "h"), // g.sub.sub.domain.tld -> h.sub.sub.domain.tld
);
D_EXTEND("sub.domain.tld",
  A("@", "127.0.0.7"), // sub.domain.tld
  CNAME("i", "j"), // i.sub.domain.tld -> j.sub.domain.tld
);
```

{% endcode %}

This will end up in the following modifications: (This output assumes the `--full` flag)

```
******************** Domain: domain.tld
----- Getting nameservers from: cloudflare
----- DNS Provider: cloudflare...7 corrections
#1: CREATE A aaa.domain.tld 127.0.0.3
#2: CREATE A bbb.sub.domain.tld 127.0.0.4
#3: CREATE A ccc.sub.domain.tld 127.0.0.5
#4: CREATE A ddd.sub.sub.domain.tld 127.0.0.6
#5: CREATE A sub.domain.tld 127.0.0.7
#6: CREATE A www.domain.tld 127.0.0.2
#7: CREATE A domain.tld 127.0.0.1
#8: CREATE CNAME a.domain.tld b.domain.tld.
#9: CREATE CNAME c.domain.tld d.domain.tld.
#10: CREATE CNAME e.sub.domain.tld f.sub.domain.tld.
#11: CREATE CNAME g.sub.sub.domain.tld h.sub.sub.domain.tld.
#12: CREATE CNAME i.sub.domain.tld j.sub.domain.tld.
```

ProTips: `D_EXTEND()` permits you to create very complex and sophisticated configurations, but you shouldn't. Be nice to the next person that edits the file, who may not be as expert as yourself. Enhance readability by putting any `D_EXTEND()` statements immediately after the original [`D()`](/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d.md), like in above example. Avoid the temptation to obscure the addition of records to existing domains with randomly placed `D_EXTEND()` statements. Don't build up a domain using loops of `D_EXTEND()` statements. You'll be glad you didn't.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.dnscontrol.org/~/revisions/Uy3v06HuP9Hvf4EPf9c7/language-reference/top-level-functions/d_extend.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.