Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="7-12  16"
{!> ../../docs_src/header_param_models/tutorial001_py310.py!}
```

////

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">

  // the default priority for pods that do not have any priority class.
  // Only one PriorityClass can be marked as `globalDefault`. However, if more than
  // one PriorityClasses exists with their `globalDefault` field set to true,
  // the smallest value of such global default PriorityClasses will be used as the default priority.
  // +optional
  optional bool globalDefault = 3;

    @Synchronized get() {
      if (field == null && started) {
        field = ServerSocketFactory.getDefault() // Build the default value lazily.
      }
      return field
    }

    @Synchronized set(value) {
      check(!started) { "serverSocketFactory must not be set after start()" }
      field = value
    }

  private var serverSocket: ServerSocket? = null

find the definition of xxx.  If xxx is a type, cgo replaces C.xxx with
a Go translation.  C arithmetic types translate to precisely-sized Go
arithmetic types.  A C struct translates to a Go struct, field by
field; unrepresentable fields are replaced with opaque byte arrays.  A
C union translates into a struct containing the first union member and
perhaps additional padding.  C arrays become Go arrays.  C pointers

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

//// tab | Python 3.10+

```Python hl_lines="2  8"
{!> ../../docs_src/body_nested_models/tutorial005_py310.py!}
```

////

		}
		ret.QuoteEscape = []rune(args.QuoteEscapeCharacter)[0]
		ret.FieldsPerRecord = -1
		// If LazyQuotes is true, a quote may appear in an unquoted field and a
		// non-doubled quote may appear in a quoted field.
		ret.LazyQuotes = true
		// We do not trim leading space to keep consistent with s3.
		ret.TrimLeadingSpace = false
		ret.ReuseRecord = true
		return ret
	}

In the examples we use a `MSS` type, which is a `map[string]string` that is `msgp` serializable.

```go
    handler := func(request *grid.MSS) (*grid.MSS, *grid.RemoteErr) {
        fmt.Println("Got request with field", request["myfield"])
        // Do something with payload
        return NewMSSWith(map[string]string{"result": "ok"}), nil
    }
	
    // Create a typed handler.

}

// MetricSpec specifies how to scale based on a single metric
// (only `type` and one other matching field should be set at once).
message MetricSpec {
  // type is the type of metric source.  It should be one of "ContainerResource", "External",
  // "Object", "Pods" or "Resource", each mapping to a matching field in the object.
  // Note: "ContainerResource" type is available on when the feature-gate
  // HPAContainerMetrics is enabled

  fmt.Printf("%v\n ", mv.Value)
}
```

output:
```
map[desc:RGB colors:[red green blue]]
map[desc:CMYK colors:[cyan magenta yellow black]]
```

likewise, increasing depth level to `3` yields:
```
red
green
blue
cyan
magenta
yellow
black
```

optionally, kev:value pairs can be emitted as an individual struct:
```go

// Only changing meaning of fields requires a version bump.
// bucketMetadataFormat refers to the format.
// bucketMetadataVersion can be used to track a rolling upgrade of a field.
type BucketMetadata struct {
	Name                        string
	Created                     time.Time
	LockEnabled                 bool // legacy not used anymore.
	PolicyConfigJSON            []byte