doc: explain how to use composite types properly (#4136)

doc/md/migration/domain.mdx

@@ -4,14 +4,15 @@ id: domain
 slug: domain-types
 ---
 
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
 import InstallationInstructions from '../components/_installation_instructions.mdx';
 
-
 PostgreSQL domain types are user-defined data types that extend existing ones, allowing you to add constraints that
 restrict the values they can hold. Setting a field type as a domain type enables you to enforce data integrity and
 validation rules at the database level.
 
-This guide explains how to define a schema field type as a domain type in your Ent schema and configure the migration
+This guide explains how to define a schema field type as a domain type in your Ent schema and configure the schema migration
 to manage both the domains and the Ent schema as a single migration unit using Atlas.
 
 :::info [Atlas Pro Feature](https://atlasgo.io/features#pro-plan)
@@ -47,6 +48,9 @@ data source. Follow the steps below to configure this for your project:
 1\. Create a `schema.sql` that defines the necessary domain type. In the same way, you can configure the domain type in
    [Atlas Schema HCL language](https://atlasgo.io/atlas-schema/hcl-types#domain):
 
+<Tabs>
+<TabItem value={"sql"} label={"Using SQL"}>
+
 ```sql title="schema.sql"
 CREATE DOMAIN us_postal_code AS TEXT
 CHECK(
@@ -55,6 +59,25 @@ CHECK(
 );
 ```
 
+</TabItem>
+<TabItem value={"hcl"} label={"Using HCL"}>
+
+```hcl title="schema.hcl"
+schema "public" {}
+
+domain "us_postal_code" {
+  schema = schema.public
+  type   = text
+  null   = true
+  check "us_postal_code_check" {
+    expr = "((VALUE ~ '^\\d{5}$'::text) OR (VALUE ~ '^\\d{5}-\\d{4}$'::text))"
+  }
+}
+```
+
+</TabItem>
+</Tabs>
+
 2\. In your Ent schema, define a field that uses the domain type only in PostgreSQL dialect:
 
 ```go title="ent/schema/user.go" {5-7}