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Provide normative guidance on function/option/option value impl. #925

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Merged
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Nov 14, 2024
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Provide normative guidance on function/option/option value impl. #925

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Provide normative guidance on allowing optional options, values, and …
aphillips Nov 6, 2024
eafc745
Update spec/registry.md
aphillips Nov 6, 2024
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Define _accept_ and use that term
aphillips Nov 8, 2024
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aphillips Nov 8, 2024
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aphillips Nov 8, 2024
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aphillips Nov 10, 2024
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Address comments around function namespacing
aphillips Nov 10, 2024
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Address 2024-11-11 telecon comments
aphillips Nov 11, 2024
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Add _Unsupported Operation_ error
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35 changes: 29 additions & 6 deletions spec/registry.md
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@@ -1,11 +1,34 @@
# MessageFormat 2.0 Default Function Registry

This section describes the functions for which each implementation MUST provide
a _function handler_ to be conformant with this specification.

Implementations MAY implement additional _functions_ or additional _options_.
In particular, implementations are encouraged to provide feedback on proposed
_options_ and their values.
This section defines the **standard** _functions_ which are REQUIRED for conformance with this specification,
along with **optional** _functions_ that SHOULD be implemented to support
additional functionality.

Implementations MUST define and support each **standard** _function_ and
MUST accept all _options_ and _option_ values defined as **standard** listed in this specification.

When defined and supported by an implementation, each **optional** _function_
MUST accept all _options_ and _option_ values listed as **standard** in this specification.

Implementations SHOULD implement _options_ and _option_ values that are marked as **optional**.

Implementations MAY implement _functions_ not defined in this specification.
Such functions MUST use an implementation-defined _namespace_.
In addition, implementations are encouraged to provide mechanisms for users to
register and use user-defined _functions_ and their associated _functional handlers_.

Implementations MAY implement additional _options_ not defined here.
Such _options_ MUST use an implementation-specific _namespace_.

Implementations MAY implement additional _option_ values for _options_ defined here,
although care needs to be exercised to ensure interoperability
and to avoid collisions with future standardization.
There is no namespace mechanism for _option_ values,
however, the [stability policy](#stability-policy) for this specification
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@macchiati macchiati Nov 8, 2024

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I don't see that the stability policy that this points to only allows a-z, A-Z, and 0-9 in option values. Does that mean we couldn't have a standard future function option that took fairly liberal string options like prefex=|β/γ| ?

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@aphillips aphillips Nov 8, 2024 •
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The stability policy says specifically:

Updates to this specification will only reserve, define, or require function names or function option names consisting of characters in the ranges a-z, A-Z, and 0-9. All other names in these categories are reserved for the use of implementations or users.

String option values can include wide ranging literals. This is meant to restrict enumerated keywords. Note too that the restriction is to option/function names, not values. We should probably consider amending this policy in an appropriate way. I will add an issue and agenda item to that effect.

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@eemeli eemeli Nov 10, 2024

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For clarity, we should probably update the stability policy text to refer to "identifiers" rather than "names" in that phrase.

permits only the ranges a-z, A-Z, and 0-9 in _option_ values.
Implementation-defined values SHOULD use a distinguishing character
or character sequence, such as by prefixing with a `_` U+005F LOW LINE,
to ensure that they don't collide with future standardization.
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@eemeli eemeli Nov 10, 2024

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If this is desirable, then we should update the stability policy to ensure that future standardization won't be able to use a _ in option values.

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@aphillips aphillips Nov 10, 2024

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Agreed. I will make a PR for that.

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@eemeli eemeli Nov 10, 2024

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See #929.


> [!NOTE]
> The [Stability Policy](/spec#stability-policy) allows for updates to
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