Change month microformat from "m" to "mo" in narrow style formatting and fix micro format tense logic

README.md

@@ -273,7 +273,7 @@ This will used to determine the length of the unit names. This value is passed t
 | relative   | narrow         | in 1 mo.                 |
 | duration   | long           | 1 month, 2 days, 4 hours |
 | duration   | short          | 1 mth, 2 days, 4 hr      |
-| duration   | narrow         | 1m 2d 4h                 |
+| duration   | narrow         | 1mo 2d 4h                |
 
 ##### second, minute, hour, weekday, day, month, year, timeZoneName
 

src/duration-format-ponyfill.ts

@@ -110,7 +110,15 @@ export default class DurationFormat {
           : unitStyle === 'numeric'
           ? {}
           : {style: 'unit', unit: nfUnit, unitDisplay: unitStyle}
-      list.push(new Intl.NumberFormat(locale, nfOpts).format(value))
+
+      let formattedValue = new Intl.NumberFormat(locale, nfOpts).format(value)
+
+      // Custom handling for narrow month formatting to use "mo" instead of "m"
+      if (unit === 'months' && (unitStyle === 'narrow' || (style === 'narrow' && formattedValue.endsWith('m')))) {
+        formattedValue = formattedValue.replace(/(\d+)m$/, '$1mo')
+      }
+
+      list.push(formattedValue)
     }
     return new ListFormat(locale, {
       type: 'unit',

src/relative-time-element.ts

@@ -170,7 +170,11 @@ export class RelativeTimeElement extends HTMLElement implements Intl.DateTimeFor
     if (format === 'micro') {
       duration = roundToSingleUnit(duration)
       empty = microEmptyDuration
-      if ((this.tense === 'past' && duration.sign !== -1) || (this.tense === 'future' && duration.sign !== 1)) {
+      // Allow month-level durations to pass through even with mismatched tense
+      if (
+        duration.months === 0 &&
+        ((this.tense === 'past' && duration.sign !== -1) || (this.tense === 'future' && duration.sign !== 1))
+      ) {
         duration = microEmptyDuration
       }
     } else if ((tense === 'past' && duration.sign !== -1) || (tense === 'future' && duration.sign !== 1)) {

test/duration-format-ponyfill.ts

@@ -37,7 +37,7 @@ suite('duration format ponyfill', function () {
       locale: 'en',
       style: 'narrow',
       parts: [
-        {type: 'element', value: '1m'},
+        {type: 'element', value: '1mo'},
         {type: 'literal', value: ' '},
         {type: 'element', value: '2d'},
         {type: 'literal', value: ' '},
@@ -92,6 +92,20 @@ suite('duration format ponyfill', function () {
         {type: 'element', value: '8s'},
       ],
     },
+    {
+      duration: 'P1M2DT3M30S',
+      locale: 'en',
+      style: 'narrow',
+      parts: [
+        {type: 'element', value: '1mo'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '2d'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '3m'},
+        {type: 'literal', value: ' '},
+        {type: 'element', value: '30s'},
+      ],
+    },
   ])
 
   for (const {duration, locale, parts, ...opts} of tests) {

test/relative-time.js

@@ -561,6 +561,17 @@ suite('relative-time', function () {
       await Promise.resolve()
       assert.equal(time.shadowRoot.textContent, '1d')
     })
+
+    test('micro formats months', async () => {
+      const datetime = new Date()
+      datetime.setMonth(datetime.getMonth() - 2)
+      const time = document.createElement('relative-time')
+      time.setAttribute('tense', 'past')
+      time.setAttribute('datetime', datetime)
+      time.setAttribute('format', 'micro')
+      await Promise.resolve()
+      assert.equal(time.shadowRoot.textContent, '2mo')
+    })
   })
 
   suite('[tense=future]', function () {
@@ -1941,7 +1952,7 @@ suite('relative-time', function () {
         datetime: '2022-09-24T14:46:00.000Z',
         tense: 'future',
         format: 'micro',
-        expected: '1m',
+        expected: '1mo',
       },
       {
         datetime: '2022-10-23T14:46:00.000Z',
@@ -1991,7 +2002,7 @@ suite('relative-time', function () {
         datetime: '2022-11-24T14:46:00.000Z',
         tense: 'future',
         format: 'micro',
-        expected: '1m',
+        expected: '1mo',
       },
       {
         datetime: '2023-10-23T14:46:00.000Z',
@@ -2023,7 +2034,7 @@ suite('relative-time', function () {
         datetime: '2022-11-24T14:46:00.000Z',
         tense: 'past',
         format: 'micro',
-        expected: '1m',
+        expected: '1mo',
       },
       {
         datetime: '2022-10-25T14:46:00.000Z',
@@ -2073,7 +2084,7 @@ suite('relative-time', function () {
         datetime: '2022-09-23T14:46:00.000Z',
         tense: 'past',
         format: 'micro',
-        expected: '1m',
+        expected: '1mo',
       },
       {
         datetime: '2021-10-25T14:46:00.000Z',
@@ -2178,13 +2189,13 @@ suite('relative-time', function () {
       {
         datetime: '2021-10-30T14:46:00.000Z',
         format: 'elapsed',
-        expected: '11m 29d',
+        expected: '11mo 29d',
       },
       {
         datetime: '2021-10-30T14:46:00.000Z',
         format: 'elapsed',
         precision: 'month',
-        expected: '11m',
+        expected: '11mo',
       },
       {
         datetime: '2021-10-29T14:46:00.000Z',