> For the complete documentation index, see [llms.txt](https://php-fhir-tools.ardenexal.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://php-fhir-tools.ardenexal.net/models/namespaces.md).

# Namespace Organization

Generated classes live under the root namespace `Ardenexal\FHIRTools\Component\Models\` and are grouped per FHIR version (`R4`, `R4B`, `R5`). Each version namespace carries the same set of subfolders:

| Subfolder   | Namespace segment | Contents                                     | Example class                         |
| ----------- | ----------------- | -------------------------------------------- | ------------------------------------- |
| `Resource`  | `…\R4\Resource`   | FHIR resources                               | `PatientResource`                     |
| `DataType`  | `…\R4\DataType`   | Complex data types                           | `HumanName`, `Address`                |
| `Primitive` | `…\R4\Primitive`  | Version-specific primitives                  | `StringPrimitive`, `BooleanPrimitive` |
| `Enum`      | `…\R4\Enum`       | Required ValueSet enums                      | `AdministrativeGender`                |
| `Extension` | `…\R4\Extension`  | Named extensions defined by the core spec    | `ADUseExtension`                      |
| `Profile`   | `…\R4\Profile`    | Constraint profiles defined by the core spec | `ActualGroupProfile`                  |

A small set of shared primitives lives **outside** the version folders, directly under `Ardenexal\FHIRTools\Component\Models\Primitive` (for example `FHIRDate`, `FHIRDateTime`, `FHIRInstant`, `FHIRTime`). These are version-agnostic and reused across R4/R4B/R5.

```php
use Ardenexal\FHIRTools\Component\Models\R4\Resource\PatientResource;
use Ardenexal\FHIRTools\Component\Models\R4\DataType\HumanName;
use Ardenexal\FHIRTools\Component\Models\R4\Primitive\StringPrimitive;
use Ardenexal\FHIRTools\Component\Models\R4\Enum\AdministrativeGender;
```

## Backbone elements

A backbone element is an inline nested structure defined within a single resource (for example `Patient.contact`). Generated backbone classes are nested in a sub-namespace named after their parent resource, so they never collide with same-named backbones on other resources:

```
R4/Resource/
├── PatientResource.php          → …\R4\Resource\PatientResource
└── Patient/
    ├── PatientContact.php        → …\R4\Resource\Patient\PatientContact
    ├── PatientCommunication.php  → …\R4\Resource\Patient\PatientCommunication
    └── PatientLink.php           → …\R4\Resource\Patient\PatientLink
```

```php
use Ardenexal\FHIRTools\Component\Models\R4\Resource\Patient\PatientContact;
```

{% hint style="danger" %}
Everything under `src/Component/Models/src/` is generated output. Never hand-edit it — regenerate with `fhir:generate`. See [Generated Output Structure](/code-generation/output-structure.md).
{% endhint %}

Implementation Guide classes are generated into a separate `IG/` tree, not these version folders — see [Generating Implementation Guides](/code-generation/implementation-guides.md).


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