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Work in progress on better docs (added docs for interfaces and unions)
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# Interfaces
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In GraphQL an Interface is an abstract type that includes a certain set of fields that a
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type must include to implement the interface.
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In **graphql-php** interface type is an instance of `GraphQL\Type\Definition\InterfaceType`
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(or one of it subclasses) which accepts configuration array in constructor:
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```php
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use GraphQL\Type\Definition\InterfaceType;
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use GraphQL\Type\Definition\Type;
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$characterInterface = new InterfaceType([
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'name' => 'Character',
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'description' => 'A character in the Star Wars Trilogy',
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'fields' => [
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'id' => [
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'type' => Type::nonNull(Type::string()),
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'description' => 'The id of the character.',
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],
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'name' => [
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'type' => Type::string(),
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'description' => 'The name of the character.'
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]
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],
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'resolveType' => function ($obj) {
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if ($obj->type === 'human') {
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return MyTypes::human();
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} else {
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return MyTypes::droid();
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}
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return null;
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}
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]);
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```
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# Abstract Type Resolution
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127
docs/type-system/interfaces.md
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127
docs/type-system/interfaces.md
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# Interface Type Definition
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An Interface is an abstract type that includes a certain set of fields that a
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type must include to implement the interface.
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In **graphql-php** interface type is an instance of `GraphQL\Type\Definition\InterfaceType`
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(or one of it subclasses) which accepts configuration array in constructor:
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```php
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use GraphQL\Type\Definition\InterfaceType;
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use GraphQL\Type\Definition\Type;
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$character = new InterfaceType([
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'name' => 'Character',
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'description' => 'A character in the Star Wars Trilogy',
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'fields' => [
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'id' => [
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'type' => Type::nonNull(Type::string()),
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'description' => 'The id of the character.',
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],
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'name' => [
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'type' => Type::string(),
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'description' => 'The name of the character.'
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]
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],
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'resolveType' => function ($value) {
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if ($value->type === 'human') {
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return MyTypes::human();
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} else {
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return MyTypes::droid();
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}
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}
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]);
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```
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This example uses **inline** style for Interface definition, but there are also
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[other styles](/type-system/#type-definition-styles) (using inheritance or composition).
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# Configuration options
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Constructor of InterfaceType accepts an array. Below is a full list of allowed options:
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Option | Type | Notes
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------ | ---- | -----
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name | `string` | **Required.** Unique name of this interface type within Schema
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fields | `array` | **Required.** List of fields required to be defined by interface implementors. Same as [Fields for Object Type](#)
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description | `string` | Plain-text description of this type for clients (e.g. used by [GraphiQL](https://github.com/graphql/graphiql) for auto-generated documentation)
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resolveType | `callback` returning instance of `ObjectType` | **function($value, $context, GraphQL\Type\Definition\ResolveInfo $info)** Any `callable` that receives `$value` from resolver of the parent field and returns concrete interface implementor for that `$value`.
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# Implementing interface
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To implement the Interface simply add it to **interfaces** array of Object Type definition:
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```php
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$humanType = new ObjectType([
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'name' => 'Human',
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'fields' => [
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'id' => [
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'type' => Type::nonNull(Type::string()),
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'description' => 'The id of the character.',
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],
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'name' => [
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'type' => Type::string(),
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'description' => 'The name of the character.'
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]
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],
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'interfaces' => [
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$character
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]
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]);
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```
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Note that Object Type must include all fields of interface with exact same types
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(including **nonNull** specification) and arguments.
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The only exception is when object's field type is more specific than the type of this field defined in interface
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(see [Covariant return types for interface fields](#covariant-return-types-for-interface-fields) below)
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# Covariant return types for interface fields
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Object types implementing interface may change field type to more specific.
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Example:
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```
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interface A {
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field1: A
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}
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type B implements A {
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field1: B
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}
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```
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# Sharing Interface fields
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Since every Object Type implementing an Interface must have the same set of fields - it often makes
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sense to re-use field definitions of Interface in Object Types:
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```php
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$humanType = new ObjectType([
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'name' => 'Human',
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'interfaces' => [
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$character
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],
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'fields' => [
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'height' => Type::float(),
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$character->getField('id'),
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$character->getField('name')
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]
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]);
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```
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In this case field definitions are created only once (as a part of Interface Type) and then
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re-used by all interface implementors. It can save several microseconds and memory + ensures that
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field definitions of Interface and implementors are always in sync.
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Yet it creates a problem with resolution of such fields. There are two ways how shared fields could
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be resolved:
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1. If field resolution algorithm is the same for all Interface implementors - you can simply add
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**resolve** option to field definition in Interface itself.
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2. If field resolution varies from implementor to implementor - you can specify **resolveField**
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option in [Object Type config](/type-system/object-types/#configuration-options) and handle field
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resolutions there
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(Note: **resolve** option in field definition has precedence over **resolveField** option in object type definition)
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# Interface role in data fetching
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The only responsibility of interface in Data Fetching process is to return concrete Object Type
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for given `$value` in **resolveType**. Then resolution of fields is delegated to resolvers of this
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concrete Object Type.
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If **resolveType** option is omitted, **graphql-php** will loop through all interface implementors and
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use their **isTypeOf** callback to pick the first suitable one. This is obviously less efficient
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than single **resolveType** call. So it is recommended to define **resolveType** whenever possible.
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36
docs/type-system/unions.md
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36
docs/type-system/unions.md
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# Union Type Definition
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A Union is an abstract type that simply enumerates other Object Types.
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Value of Union Type is actually a value of one of included Object Types.
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In **graphql-php** union type is an instance of `GraphQL\Type\Definition\UnionType`
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(or one of it subclasses) which accepts configuration array in constructor:
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```php
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$searchResultType = new UnionType([
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'name' => 'SearchResult',
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'types' => [
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MyTypes::story(),
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MyTypes::user()
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];
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'resolveType' => function($value) {
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if ($value->type === 'story') {
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return MyTypes::story();
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} else {
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return MyTypes::user();
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}
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}
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]);
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```
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This example uses **inline** style for Union definition, but there are also
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[other styles](/type-system/#type-definition-styles) (using inheritance or composition).
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# Configuration options
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Constructor of UnionType accepts an array. Below is a full list of allowed options:
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Option | Type | Notes
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------ | ---- | -----
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name | `string` | **Required.** Unique name of this interface type within Schema
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types | `array` | **Required.** List of Object Types included in this Union. Note that you can't create a Union type out of Interfaces or other Unions.
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description | `string` | Plain-text description of this type for clients (e.g. used by [GraphiQL](https://github.com/graphql/graphiql) for auto-generated documentation)
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resolveType | `callback` returning instance of `ObjectType` | **function($value, $context, GraphQL\Type\Definition\ResolveInfo $info)** Any `callable` that receives `$value` from resolver of the parent field and returns Object Type for that `$value`.
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@ -8,8 +8,10 @@ pages:
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- Scalar Types: type-system/scalar-types.md
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- Enumeration Types: type-system/enum-types.md
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- Lists and Non-Null: type-system/lists-and-nonnulls.md
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- Interfaces and Unions: type-system/abstract-types.md
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- Interfaces: type-system/interfaces.md
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- Unions: type-system/unions.md
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- Defining Schema: type-system/schema.md
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- Custom Metadata: type-system/metadata.md
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- Data Fetching: data-fetching.md
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- Best Practices: best-practices.md
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- Complementary Tools: complementary-tools.md
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