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Clarification to default bidi strategy #968

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Clarification to default bidi strategy #968

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76ca624
Add note elaborating on what the directionality of the resolved value…
catamorphism Dec 9, 2024
bb37ee7
Avoid breaking up algorithm steps with NOTE
catamorphism Dec 9, 2024
dd52758
Incorporate feedback from Eemeli
catamorphism Dec 16, 2024
b78ec62
Avoid repetition
catamorphism Dec 16, 2024
80c5b25
Rewrite to not define an auxiliary function
catamorphism Dec 16, 2024
fd6be39
Incorporate feedback from Eemeli
catamorphism Dec 20, 2024
7896fbf
Add directionality methods to MessageValue
catamorphism Dec 20, 2024
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33 changes: 30 additions & 3 deletions spec/formatting.md
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Original file line number Diff line number Diff line change
Expand Up @@ -940,11 +940,12 @@ The _Default Bidi Strategy_ is defined as follows:
Note that this is normally the empty string.
1. Append `fmt` to `out`.
1. Else:
1. Let `fmt` be the formatted string representation of the _resolved value_ of `part`.
1. Let `dir` be the directionality of `fmt`,
1. Let `resval` be the _resolved value_ of `part`.
1. Let `fmt` be the formatted string representation of `resval`.
1. Let `dir` be the directionality of `resval`,
one of « `'LTR'`, `'RTL'`, `'unknown'` », with the same meanings as for `msgdir`.
1. Let the boolean value `isolate` be
True if the `u:dir` _option_ of the _resolved value_ of `part` has a value other than `'inherit'`,
True if the `u:dir` _option_ of `resval` has a value other than `'inherit'`,
or False otherwise.
1. If `dir` is `'LTR'`:
1. If `msgdir` is `'LTR'` and `isolate` is False:
Expand All @@ -963,4 +964,30 @@ The _Default Bidi Strategy_ is defined as follows:
1. Append U+2069 POP DIRECTIONAL ISOLATE to `out`.
1. Emit `out` as the formatted output of the message.

> [!NOTE]
> A _resolved value_ is derived from an _expression_
> together with a _formatting context_.)
> An implementation can use
> a representation of _resolved values_ that tracks
> everything needed to determine the directionality
> of the formatted string representation
> of a _resolved value_.
> This can be accomplished by incorporating
> the `isolate` flag used in step 2(iii),
> as well as the separate directionality annotation
> (one of « `'LTR'`, `'RTL'`, `'unknown'` »),
> into the representation of _resolved values_.
> Each _function handler_ can have its own means
> for determining the directionality annotation
> on the _resolved value_ it returns.
> Alternately, an implementation could simply
> determine directionality
> based on the locale.
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On further consideration, does this perhaps belong more appropriately in the section defining resolved values?

Specifically, I think we ought to expand a bit the paragraph starting on line 133 with something like this:

 In a _pattern_, the _resolved value_ of an _expression_ or _markup_ is used in its _formatting_.
+To account for the _Default Bidi Strategy_,
+the _resolved value_ of each _expression_ _placeholder_
+SHOULD include information about the directionality of its formatted string representation,
+as well as information about whether its formatted representation
+requires isolation from the surrounding text.

With that in place, this note could be simplified quite a bit, or even left out entirely.

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This is pretty good, but I wouldn't limit it to the default bidi strategy, nor would I necessarily limit it to placeholders (other expressions might have a directionality so that the direction is commutative across assignments). Perhaps:

The resolved value of each expression
SHOULD include the string direction
of its formatted string representation,
as well as information about whether the message author
wants to suppress or require isolation from the surrounding message text,
such as is found in the Default Bidi Strategy.

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Note that resolved value is an implementation-internal thing, and is therefore not expected to have public visibility during formatting. This means that attaching any normative requirements on it ought to be explicitly connected to some spec-defined consumer of that information, i.e. the Default Bidi Strategy.

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I made these changes. Also modified the example MessageValue definition to show what the directionality methods could look like.


> [!NOTE]
> Directionality SHOULD NOT be determined by introspecting
> the character sequence in the formatted string representation
> of `resval`.


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