# `Dicom.PrivateTag`
[🔗](https://github.com/Balneario-de-Cofrentes/dicom/blob/v0.9.1/lib/dicom/private_tag.ex#L1)

Private tag validation per DICOM PS3.6 Section 6.1.2.1.

Private tags use odd-numbered groups (excluding 0x0001). Within each
private group, a "block" is identified by a creator element at
`(gggg,00xx)` where `xx` ranges from `0x10` to `0xFF`. The creator
element has VR LO and its value identifies the definer of the block.

Private data elements in block `xx` occupy `(gggg,xx00)` through
`(gggg,xxFF)`. Every private data element must have a corresponding
creator element for the data set to be valid.

## Examples

    iex> Dicom.PrivateTag.private?({0x0009, 0x1001})
    true

    iex> Dicom.PrivateTag.private_block({0x0009, 0x1001})
    16

    iex> Dicom.PrivateTag.creator_tag({0x0009, 0x1001})
    {0x0009, 0x0010}

# `tag`

```elixir
@type tag() :: Dicom.DataElement.tag()
```

# `creator_element?`

```elixir
@spec creator_element?(tag()) :: boolean()
```

Returns true if the tag is a private creator element.

Creator elements occupy element numbers 0x0010 through 0x00FF within
a private (odd) group.

# `creator_for`

```elixir
@spec creator_for(Dicom.DataSet.t(), tag()) :: String.t() | nil
```

Returns the creator string for a private data element, or nil.

Looks up the creator element `(gggg,00xx)` in the data set and returns
its value. Returns nil if the tag is not private or the creator is absent.

# `creator_tag`

```elixir
@spec creator_tag(tag()) :: tag()
```

Returns the creator tag for a given private tag.

For a data element `(gggg,xxyy)`, the creator is `(gggg,00xx)`.
For a creator element `(gggg,00xx)`, returns the tag unchanged.

# `private?`

```elixir
@spec private?(tag()) :: boolean()
```

Returns true if the tag is in a private group.

Private groups have odd group numbers, excluding group 0x0001
(the DICOM Command group).

# `private_block`

```elixir
@spec private_block(tag()) :: non_neg_integer()
```

Extracts the block number from a private tag's element number.

For creator elements `(gggg,00xx)` the block is `xx`.
For data elements `(gggg,xxyy)` the block is the high byte `xx`.

# `validate_creators`

```elixir
@spec validate_creators(Dicom.DataSet.t()) ::
  {:ok, Dicom.DataSet.t()} | {:error, [{tag(), :missing_creator}]}
```

Validates that every private data element has a corresponding creator.

Scans all elements in the data set. For each private data element
(element > 0x00FF in an odd group), checks that a creator element
exists at `(gggg,00xx)`.

Returns `{:ok, data_set}` when all creators are present, or
`{:error, [{tag, :missing_creator}]}` listing every orphaned element.

---

*Consult [api-reference.md](api-reference.md) for complete listing*