> 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/serialization/context.md).

# Configuring Serialization Behavior

`FHIRSerializationContext` is an immutable, chainable value object that configures how serialization behaves — validation mode, unknown-element policy, debug info, and more. Start from a format factory (`forJson()` / `forXml()`), chain `with*()` calls (each returns a new instance), then pass the result to a serialize/deserialize method via `toSymfonyContext()`.

```php
<?php

use Ardenexal\FHIRTools\Component\Serialization\Context\FHIRSerializationContext;

$context = FHIRSerializationContext::forJson()
    ->withValidationMode(FHIRSerializationContext::VALIDATION_STRICT)
    ->withUnknownElementPolicy(FHIRSerializationContext::UNKNOWN_POLICY_ERROR)
    ->withDebugInfo(true);

$json = $serializer->serializeToJson($patient, $context->toSymfonyContext());
```

{% hint style="info" %}
The context is immutable — every `with*()` call returns a **new** instance and leaves the original unchanged. Always capture the return value.
{% endhint %}

If the snippet above covers your needs — strict validation, rejecting unknown elements — you can stop here. The sections below document the full option surface.

## Factories and modifiers

| Member                                | Effect                                                                         |
| ------------------------------------- | ------------------------------------------------------------------------------ |
| `FHIRSerializationContext::forJson()` | Base context for JSON.                                                         |
| `FHIRSerializationContext::forXml()`  | Base context for XML (XML namespaces enabled).                                 |
| `withFormat(string)`                  | `FORMAT_JSON` or `FORMAT_XML`.                                                 |
| `withValidationMode(string)`          | `VALIDATION_STRICT` or `VALIDATION_LENIENT`.                                   |
| `withUnknownElementPolicy(string)`    | `UNKNOWN_POLICY_IGNORE`, `UNKNOWN_POLICY_ERROR`, or `UNKNOWN_POLICY_PRESERVE`. |
| `withDebugInfo(bool)`                 | Toggle debug-info collection.                                                  |
| `withPerformanceOptimization(bool)`   | Skip non-essential validation for speed.                                       |
| `withCustomOptions(array)`            | Merge arbitrary Symfony serializer options.                                    |
| `toSymfonyContext()`                  | Convert to the `array` accepted by the serialize/deserialize methods.          |

Convenience constructors bundle common combinations: `withStrictValidation()`, `withLenientValidation()`, `withDebugging()`, `preservingUnknownElements()`, `erroringOnUnknownElements()`.

## Validation modes

The constructor default is **lenient** (`VALIDATION_LENIENT`). The mode is validated on construction — an invalid value throws `\InvalidArgumentException`.

| Mode    | Constant             | Behavior                                                                                                                                |
| ------- | -------------------- | --------------------------------------------------------------------------------------------------------------------------------------- |
| Strict  | `VALIDATION_STRICT`  | Full FHIR validation; `withStrictValidation()` also enables reference validation and does not skip non-essential checks.                |
| Lenient | `VALIDATION_LENIENT` | Relaxed validation for development/performance; `withLenientValidation()` skips non-essential checks and disables reference validation. |

```php
<?php

$strict = FHIRSerializationContext::forJson()->withStrictValidation();
$lenient = FHIRSerializationContext::forJson()->withLenientValidation();
```

For raw, performance-tuned context arrays there is also `FHIRSerializationContextFactory` (`createJsonContext`, `createXmlContext`, `createStrictContext`, `createLenientContext`, `createPerformanceContext`, `createDebugContext`), each accepting an `$overrides` array. The service uses this factory internally; you rarely call it directly.

## Unknown-element policies

Controls what happens when an element in the payload is not recognised. Default is `UNKNOWN_POLICY_IGNORE`.

| Policy   | Constant                  | Behavior                                      |
| -------- | ------------------------- | --------------------------------------------- |
| Ignore   | `UNKNOWN_POLICY_IGNORE`   | Silently drop unknown elements (default).     |
| Error    | `UNKNOWN_POLICY_ERROR`    | Reject unknown elements.                      |
| Preserve | `UNKNOWN_POLICY_PRESERVE` | Keep unknown elements through the round-trip. |

```php
<?php

$preserving = FHIRSerializationContext::forJson()->preservingUnknownElements();
$erroring   = FHIRSerializationContext::forJson()->erroringOnUnknownElements();
```

## Inspecting the last operation

After a serialize/deserialize call you can inspect what happened:

```php
<?php

$debug = $serializer->getDebugInfo(); // array<string, mixed>
```


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