Clarify option literalness details (#1027)

* Clarify option literalness details

Fixes #1026

* Reword description of option value literalness information

Co-authored-by: Addison Phillips <[email protected]>

* Update spec/formatting.md

Co-authored-by: Mark Davis <[email protected]>

---------

Co-authored-by: Addison Phillips <[email protected]>
Co-authored-by: Mark Davis <[email protected]>

Author: 3 people

spec/formatting.md

@@ -137,9 +137,17 @@ as well as a flag to indicate whether
 its formatted representation requires isolation
 from the surrounding text.
 
-To allow for _function handlers_ to ensure that certain _option_ values are set by _literals_,
-the _resolved value_ of each _option_ value MUST include information about 
-whether the _option_ value is a _literal_ or a _variable_.
+For each _option_ value, the _resolved value_ MUST indicate if the value
+was directly set with a _literal_, as opposed to being resolved from a _variable_.
+This is to allow _functions handlers_ to require specific _options_ to be set using _literals_.
+
+> For example, the _default functions_ `:number` and `:integer` require that the _option_
+> `select` be set with a _literal_ (`plural`, `ordinal`, or `exact`). 
+> Allowing a _variable_ in this _option_ would produce a _message_ that 
+> is impossible to translate because the set of _keys_ is tied to the _selector_ chosen.
+
+> [!NOTE]
+> Such information is irrelevant for _resolved values_ not used as the value of an _option_.
 
 The form that _resolved values_ take is implementation-dependent,
 and different implementations MAY choose to perform different levels of resolution.
@@ -329,6 +337,7 @@ the following steps are taken:
 
 6. If the call succeeds,
    resolve the value of the _expression_ as the result of that function call.
+   The value MUST NOT be marked as a literal option value.
 
    If the call fails or does not return a valid value,
    emit the appropriate _Message Function Error_ for the failure.
@@ -395,7 +404,7 @@ For each _option_:
       1. If supported, emit a _Bad Option_ error.
    1. Else:
       1. If the _option_ value consists of a _literal_:
-         1. Include that information in `rv`.
+         1. Mark `rv` as a literal option value.
       1. Set `res[id]` to be `rv`.
 1. Return `res`.