Define matching for simple integers, leave others up to implementatio…

…ns (#933)

* Define matching for simple integers, leave others up to implementations

* Add fractionDigits & maximumSignificantDigits

* Allow negative integers, rename section, drop fractionDigits

* Update spec/registry.md

---------

Co-authored-by: Addison Phillips <addison@unicode.org>

spec/registry.md

@@ -703,8 +703,8 @@ where `resolvedSelector` is the _resolved value_ of a _selector_
 and `keys` is a list of strings,
 numeric selectors perform as described below.
 
-1. Let `exact` be the JSON string representation of the numeric value of `resolvedSelector`.
-   (See [Determining Exact Literal Match](#determining-exact-literal-match) for details)
+1. Let `exact` be the serialized representation of the numeric value of `resolvedSelector`.
+   (See [Exact Literal Match Serialization](#exact-literal-match-serialization) for details)
 1. Let `keyword` be a string which is the result of [rule selection](#rule-selection) on `resolvedSelector`.
 1. Let `resultExact` be a new empty list of strings.
 1. Let `resultKeyword` be a new empty list of strings.
@@ -780,36 +780,31 @@ for examples.
 > | 27 | `other` | 27 dní |
 > | 2.4 | `many` | 2,4 dne |
 
-#### Determining Exact Literal Match
+#### Exact Literal Match Serialization
 
-> [!IMPORTANT]
-> The exact behavior of exact literal match is currently only well defined for non-zero-filled
-> integer values.
-> Functions that use fraction digits or significant digits might work in specific
-> implementation-defined ways.
-> Users should avoid depending on these types of keys in message selection in this release.
+If the numeric value of `resolvedSelector` is an integer
+and none of the following options are set for `resolvedSelector`,
+the serialized form of the numeric value MUST match the ABNF defined below for `integer`,
+representing its decimal value:
+- `minimumFractionDigits`
+- `minimumIntegerDigits`
+- `minimumSignificantDigits`
+- `maximumSignificantDigits`
+- `notation`
+- `style`
 
+```abnf
+integer = "0" / ["-"] ("1"-"9") *DIGIT
+```
 
-Number literals in the MessageFormat 2 syntax use the 
-[format defined for a JSON number](https://www.rfc-editor.org/rfc/rfc8259#section-6).
-A `resolvedSelector` exactly matches a numeric literal `key`
-if, when the numeric value of `resolvedSelector` is serialized using the format for a JSON number,
-the two strings are equal.
+Otherwise, the serialized form of the numeric value is implementation-defined.
 
-> [!NOTE]
-> The above description of numeric matching contains 
-> [open issues](https://github.com/unicode-org/message-format-wg/issues/675)
-> in the Technical Preview, since a given numeric value might be formatted in
-> several different ways under RFC8259
-> and since the effect of formatting options, such as the number of fraction
-> digits or significant digits, is not described.
-> The Working Group intends to address these issues before final release
-> with a number of design options
-> [being considered](https://github.com/unicode-org/message-format-wg/pull/859).
->
-> Users should avoid creating messages that depend on exact matching of non-integer
-> numeric values.
-> Feedback, including use cases encountered in message authoring, is strongly desired.
+> [!IMPORTANT]
+> The exact behavior of exact literal match is only well defined
+> for integer values without leading zeros.
+> Functions that use fraction digits or significant digits
+> might work in specific implementation-defined ways.
+> Users should avoid depending on these types of keys in message selection.
 
 ## Date and Time Value Formatting
 

test/tests/functions/integer.json

@@ -20,14 +20,14 @@
       "exp": "hello 4"
     },
     {
-      "src": ".input {$foo :integer} .match $foo 1 {{one}} * {{other}}",
-      "params": [
-        {
-          "name": "foo",
-          "value": 1.2
-        }
-      ],
-      "exp": "one"
+      "src": ".input {$foo :integer} .match $foo 1 {{=1}} * {{other}}",
+      "params": [{ "name": "foo", "value": 1.2 }],
+      "exp": "=1"
+    },
+    {
+      "src": ".input {$foo :integer} .match $foo 1 {{=1}} one {{one}} * {{other}}",
+      "params": [{ "name": "foo", "value": 1.2 }],
+      "exp": "=1"
     },
     {
       "src": ".local $x = {1.25 :integer} .local $y = {$x :number} {{{$y}}}",