# `HL7v2.Standard.VersionDeltas`
[🔗](https://github.com/Balneario-de-Cofrentes/hl7v2/blob/v3.10.1/lib/hl7v2/standard/version_deltas.ex#L1)

Tracks field optionality changes between HL7 v2.x versions.

Currently tracks v2.7+ field deprecations (fields that became B — backward
compatibility only — in v2.7). When validating a message at v2.7 or later,
these fields should NOT be enforced as required even though the baseline
v2.5.1 schema marks them `:r` or `:c`.

HL7 does not change a field's optionality from `:o` → `:r` between versions.
What it does is retire previously required/conditional fields by marking them
`:b` (backward compatibility only) and introducing replacement fields. The
[`HL7v2.Validation.FieldRules`](`HL7v2.Validation.FieldRules`) pipeline uses
`exempt?/3` to skip required-field enforcement for known deprecations when a
message declares itself at a version where the field is no longer required.

## Currently tracked v2.7 deprecations

- `PID-13`, `PID-14` — telecom fields, replaced by `PID-40`
  (`patient_telecommunication_information`).
- `OBR-10`, `OBR-16` — collector/ordering provider, replaced by the `PRT`
  segment (and `OBR-50` for parent service identifier).
- `ORC-10`, `ORC-12` — entered_by / ordering_provider, replaced by the `PRT`
  segment.

Note: the baseline v2.5.1 schema shipped with this library currently marks
several of these deprecated fields as `:o` already, so the exemption is a
no-op for them today. The deprecation list is still enforced so that any
future schema tightening (e.g., reinstating the canonical v2.5.1 `:r`/`:c`
markings for `OBR-10`/`OBR-16`) remains safe for v2.7+ messages without
additional bookkeeping.

# `exempt?`

```elixir
@spec exempt?(binary(), pos_integer(), binary() | nil) :: boolean()
```

Returns `true` if a field is exempt from required-field enforcement at the
given version, and `false` if the field should still be required per the
baseline v2.5.1 schema.

The `version` argument should be a normalized HL7 version string (e.g.
`"2.5.1"`, `"2.7"`). Pass `nil` when the validating caller has no version
context — the function returns `false` in that case and the baseline
v2.5.1 rules apply unchanged.

## Examples

    iex> HL7v2.Standard.VersionDeltas.exempt?("PID", 13, "2.7")
    true

    iex> HL7v2.Standard.VersionDeltas.exempt?("PID", 13, "2.8")
    true

    iex> HL7v2.Standard.VersionDeltas.exempt?("PID", 13, "2.5.1")
    false

    iex> HL7v2.Standard.VersionDeltas.exempt?("PID", 5, "2.7")
    false

    iex> HL7v2.Standard.VersionDeltas.exempt?("PID", 13, nil)
    false

# `v27_deprecations`

```elixir
@spec v27_deprecations() :: [{binary(), pos_integer()}]
```

Returns all v2.7 deprecations as a list of `{segment_id, field_seq}` tuples.

Useful for documentation, introspection, and tests that want to assert the
exhaustive deprecation set without duplicating the literal.

---

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