diff --git a/src/inflection/message2/MF2Factory.hpp b/src/inflection/message2/MF2Factory.hpp
index 05ac4a0ae..a622d0de1 100644
--- a/src/inflection/message2/MF2Factory.hpp
+++ b/src/inflection/message2/MF2Factory.hpp
@@ -21,9 +21,9 @@
  * <blockquote>
  * <pre>
  * auto customRegistry = icu::message2::MFFunctionRegistry::Builder(errorCode)
- *          .adoptFormatter(FunctionName("inflect"),
+ *          .adoptFormatter(FunctionName("i:inflect"),
  *                          MF2Factory::createInflectFormatterFactory(), errorCode)
- *          .adoptSelector(FunctionName("inflect"),
+ *          .adoptSelector(FunctionName("i:inflect"),
  *                          MF2Factory::createInflectSelectorFactory(), errorCode)
  *          .build();
  *
@@ -31,7 +31,7 @@
  * auto mf1 = icu::message2::MessageFormatter::Builder(errorCode)
  *              .setFunctionRegistry(customRegistry)
  *              .setLocale(Locale::forLanguageTag("es-MX", errorCode))
- *              .setPattern("Location is {$name :inflect hello=world \
+ *              .setPattern("Location is {$name :i:inflect hello=world \
  *                           definiteness=definite number=plural \
  *                           gender=feminine}",
  *                          pe, errorCode)
@@ -40,9 +40,9 @@
  * auto mf2 = icu::message2::MessageFormatter::Builder(errorCode)
  *              .setFunctionRegistry(customRegistry)
  *              .setLocale(Locale::forLanguageTag("es-MX", errorCode))
- *              .setPattern(".local $gender = {$name :inflect \
+ *              .setPattern(".local $gender = {$name :i:inflect \
  *                                             feature=gender} \
- *                           .local $number = {$name :inflect \
+ *                           .local $number = {$name :i:inflect \
  *                                             feature=number} \
  *                           .match $gender $number \
  *                           feminine singular {{Feminine Singular {$name}}}\
@@ -83,22 +83,22 @@ class INFLECTION_CLASS_API inflection::message2::MF2Factory {
 
       /**
        * Create an implementation of icu::message2::FormatterFactory* for the
-       * :numeral function (number formatting), based on the inflection library,
+       * :i:numeral function (number formatting), based on the inflection library,
        * which can be passed to
        * icu::messsage2::MFFunctionRegistry::Builder::adoptFormatter
        * to register a custom formatter factory.
        */
       static icu::message2::FormatterFactory* createNumeralFormatterFactory(OutputMode mode = OutputMode::PLAIN);
 
-      /** Create a FormatterFactory for the :quantify function (count + unit agreement). */
+      /** Create a FormatterFactory for the :i:quantify function (count + unit agreement). */
       static icu::message2::FormatterFactory* createQuantifyFormatterFactory(OutputMode mode = OutputMode::PLAIN);
 
-      /** Create a FormatterFactory for the :list function (array → plain/and/or list). */
+      /** Create a FormatterFactory for the :i:list function (array → plain/and/or list). */
       static icu::message2::FormatterFactory* createListFormatterFactory(OutputMode mode = OutputMode::PLAIN);
 
-      /** Create a FormatterFactory for the :pronoun function. */
+      /** Create a FormatterFactory for the :i:pronoun function. */
       static icu::message2::FormatterFactory* createPronounFormatterFactory(OutputMode mode = OutputMode::PLAIN);
 
-      /** Create a SelectorFactory for the :pronoun function. */
+      /** Create a SelectorFactory for the :i:pronoun function. */
       static icu::message2::SelectorFactory* createPronounSelectorFactory();
 };
diff --git a/test/resources/inflection/message2/de_DE.xml b/test/resources/inflection/message2/de_DE.xml
index 3045e16f3..64c96ccdc 100644
--- a/test/resources/inflection/message2/de_DE.xml
+++ b/test/resources/inflection/message2/de_DE.xml
@@ -8,7 +8,7 @@
         <params>
             <param name="name" type="String"><value>Bank</value></param>
         </params>
-        <source>.local $defArticleInPreposition = {$name :inflect number=singular case=accusative to=defArticleInPreposition} .match $defArticleInPreposition
+        <source>.local $defArticleInPreposition = {$name :i:inflect number=singular case=accusative to=defArticleInPreposition} .match $defArticleInPreposition
 |in die| {{The defArticleInPreposition of '{$name}' is 'in die'.}}
 * {{The defArticleInPreposition of '{$name}' is unexpectedly '$defArticleInPreposition'.}}
 </source>
@@ -18,7 +18,7 @@
         <params>
             <param name="name" type="String"><value>Fundort</value></param>
         </params>
-        <source>.local $withDefArticleInPreposition = {$name :inflect number=singular case=dative to=withDefArticleInPreposition} .match $withDefArticleInPreposition
+        <source>.local $withDefArticleInPreposition = {$name :i:inflect number=singular case=dative to=withDefArticleInPreposition} .match $withDefArticleInPreposition
 |im Fundort| {{The withDefArticleInPreposition of '{$name}' is 'im Fundort'.}}
 * {{The withDefArticleInPreposition of '{$name}' is something else.}}
 </source>
@@ -28,7 +28,7 @@
         <params>
             <param name="name" type="String"><value>Bank</value></param>
         </params>
-        <source>The defArticleInPreposition is {$name :inflect number=singular case=accusative to=defArticleInPreposition}.</source>
+        <source>The defArticleInPreposition is {$name :i:inflect number=singular case=accusative to=defArticleInPreposition}.</source>
         <print>The defArticleInPreposition is in die.</print>
     </test>
 </message2test>
diff --git a/test/resources/inflection/message2/en_US.xml b/test/resources/inflection/message2/en_US.xml
index 1516db6e6..e403b0900 100644
--- a/test/resources/inflection/message2/en_US.xml
+++ b/test/resources/inflection/message2/en_US.xml
@@ -8,21 +8,21 @@
         <params>
             <param name="object" type="String"><value>lights</value></param>
         </params>
-        <source>The {$object} {is :inflect number=$object} on.</source>
+        <source>The {$object} {is :i:inflect number=$object} on.</source>
         <print>The lights are on.</print>
     </test>
     <test>
         <params>
             <param name="object" type="String"><value>lights</value></param>
         </params>
-        <source>{$object :inflect definiteness=definite} {is :inflect number=$object} on.</source>
+        <source>{$object :i:inflect definiteness=definite} {is :i:inflect number=$object} on.</source>
         <print>the lights are on.</print>
     </test>
     <test>
         <params>
             <param name="object" type="String"><value>light</value></param>
         </params>
-        <source>.local $num = {$object :inflect to=number} .match $num
+        <source>.local $num = {$object :i:inflect to=number} .match $num
 plural {{The {$object} are on}}
 * {{The {$object} is on}}
 </source>
@@ -32,7 +32,7 @@ plural {{The {$object} are on}}
         <params>
             <param name="object" type="String"><value>lights</value></param>
         </params>
-        <source>.local $num = {$object :inflect to=number} .match $num
+        <source>.local $num = {$object :i:inflect to=number} .match $num
 plural {{The {$object} are on}}
 * {{The {$object} is on}}
 </source>
@@ -42,7 +42,7 @@ plural {{The {$object} are on}}
         <params>
             <param name="object" type="String"><value>lights on the front porch</value></param>
         </params>
-        <source>.local $num = {$object :inflect to=number} .match $num
+        <source>.local $num = {$object :i:inflect to=number} .match $num
 plural {{The {$object} are on}}
 * {{The {$object} is on}}
 </source>
@@ -52,7 +52,7 @@ plural {{The {$object} are on}}
         <params>
             <param name="object" type="String"><value>light on the front porch</value></param>
         </params>
-        <source>.local $num = {$object :inflect to=number} .match $num
+        <source>.local $num = {$object :i:inflect to=number} .match $num
 plural {{The {$object} are on}}
 * {{The {$object} is on}}
 </source>
@@ -62,28 +62,28 @@ plural {{The {$object} are on}}
         <params>
             <param name="relationship" type="String"><value>brother</value></param>
         </params>
-        <source>I didn't find {$relationship :inflect definiteness=indefinite} in your contacts. What is your {$relationship :inflect case=genitive} name?</source>
+        <source>I didn't find {$relationship :i:inflect definiteness=indefinite} in your contacts. What is your {$relationship :i:inflect case=genitive} name?</source>
         <print>I didn't find a brother in your contacts. What is your brother’s name?</print>
     </test>
     <test>
         <params>
             <param name="relationship" type="String"><value>aunt</value></param>
         </params>
-        <source>I didn't find {$relationship :inflect definiteness=indefinite} in your contacts. What is your {$relationship :inflect case=genitive} name?</source>
+        <source>I didn't find {$relationship :i:inflect definiteness=indefinite} in your contacts. What is your {$relationship :i:inflect case=genitive} name?</source>
         <print>I didn't find an aunt in your contacts. What is your aunt’s name?</print>
     </test>
     <test>
         <params>
             <param name="oridinalNum" type="Number"><value>4</value></param>
         </params>
-        <source>Your {$oridinalNum :numeral withStyle=asWords withVariant=ordinal} meeting has been canceled</source>
+        <source>Your {$oridinalNum :i:numeral withStyle=asWords withVariant=ordinal} meeting has been canceled</source>
         <print>Your fourth meeting has been canceled</print>
     </test>
     <test>
         <params>
             <param name="count" type="Number"><value>4</value></param>
         </params>
-        <source>You have {$count :numeral withStyle=asSpokenWords} messages</source>
+        <source>You have {$count :i:numeral withStyle=asSpokenWords} messages</source>
         <print>You have 4 messages</print>
         <speak>You have four messages</speak>
     </test>
@@ -92,7 +92,7 @@ plural {{The {$object} are on}}
             <param name="n" type="Number"><value>1</value></param>
             <param name="unit" type="String"><value>day</value></param>
         </params>
-        <source>Your meeting is in {$unit :quantify withValue=$n} from now</source>
+        <source>Your meeting is in {$unit :i:quantify withValue=$n} from now</source>
         <print>Your meeting is in 1 day from now</print>
     </test>
     <test>
@@ -100,7 +100,7 @@ plural {{The {$object} are on}}
             <param name="n" type="Number"><value>2</value></param>
             <param name="unit" type="String"><value>day</value></param>
         </params>
-        <source>Your meeting is in {$unit :quantify withValue=$n} from now</source>
+        <source>Your meeting is in {$unit :i:quantify withValue=$n} from now</source>
         <print>Your meeting is in 2 days from now</print>
     </test>
     <test>
@@ -108,21 +108,21 @@ plural {{The {$object} are on}}
             <param name="n" type="Number"><value>3</value></param>
             <param name="unit" type="String"><value>church</value></param>
         </params>
-        <source>{$unit :quantify withValue=$n} were found nearby</source>
+        <source>{$unit :i:quantify withValue=$n} were found nearby</source>
         <print>3 churches were found nearby</print>
     </test>
     <test>
         <params>
             <param name="word" type="String"><value>valid</value></param>
         </params>
-        <source>{$word :inflect bogusFeature=value}</source>
+        <source>{$word :i:inflect bogusFeature=value}</source>
         <print error="U_MF_FORMATTING_ERROR"/>
     </test>
     <test>
         <params>
             <param name="word" type="String"><value>valid</value></param>
         </params>
-        <source>.local $v = {$word :inflect bogusFeature=value} .match $v
+        <source>.local $v = {$word :i:inflect bogusFeature=value} .match $v
 * {{fallback}}
 </source>
         <print error="U_MF_SELECTOR_ERROR"/>
@@ -131,14 +131,14 @@ plural {{The {$object} are on}}
         <params>
             <param name="word" type="String"><value>valid</value></param>
         </params>
-        <source>{$word :inflect to=bogus}</source>
+        <source>{$word :i:inflect to=bogus}</source>
         <print>valid</print>
     </test>
     <test>
         <params>
             <param name="word" type="String"><value>valid</value></param>
         </params>
-        <source>.local $v = {$word :inflect to=bogus} .match $v
+        <source>.local $v = {$word :i:inflect to=bogus} .match $v
 valid {{is valid}}
 * {{other}}
 </source>
@@ -146,22 +146,22 @@ valid {{is valid}}
     </test>
     <test>
         <params><param name="p" type="String"><value>her</value></param></params>
-        <source>{$p :pronoun gender=masculine}</source>
+        <source>{$p :i:pronoun gender=masculine}</source>
         <print>his</print>
     </test>
     <test>
         <params><param name="p" type="PronounConcept"><value>theirs</value></param></params>
-        <source>{$p :pronoun gender=masculine}</source>
+        <source>{$p :i:pronoun gender=masculine}</source>
         <print>his</print>
     </test>
     <test>
         <params><param name="p" type="PronounConcept"><value>he</value></param></params>
-        <source>{theirs :pronoun gender=$p}</source>
+        <source>{theirs :i:pronoun gender=$p}</source>
         <print>his</print>
     </test>
     <test>
         <params><param name="p" type="String"><value>she</value></param></params>
-        <source>.local $g = {$p :pronoun to=gender} .match $g
+        <source>.local $g = {$p :i:pronoun to=gender} .match $g
 feminine {{feminine phrase}}
 masculine {{masculine phrase}}
 * {{other phrase}}
@@ -170,7 +170,7 @@ masculine {{masculine phrase}}
     </test>
     <test>
         <params><param name="p" type="String"><value>garbage</value></param></params>
-        <source>{$p :pronoun}</source>
+        <source>{$p :i:pronoun}</source>
         <print error="U_MF_FORMATTING_ERROR"/>
     </test>
     <test>
@@ -178,7 +178,7 @@ masculine {{masculine phrase}}
             <param name="p" type="String"><value>her</value></param>
             <param name="obj" type="String"><value>cat</value></param>
         </params>
-        <source>{$p :pronoun to=gender withReferent=$obj}</source>
+        <source>{$p :i:pronoun to=gender withReferent=$obj}</source>
         <print error="U_MF_FORMATTING_ERROR"/>
     </test>
     <test>
@@ -189,7 +189,7 @@ masculine {{masculine phrase}}
                 <value constraint="third singular genitive">xyr</value>
             </param>
         </params>
-        <source>{$np :pronoun case=accusative} {$np :pronoun}</source>
+        <source>{$np :i:pronoun case=accusative} {$np :i:pronoun}</source>
         <print>xem xe</print>
     </test>
 </message2test>
diff --git a/test/resources/inflection/message2/es_MX.xml b/test/resources/inflection/message2/es_MX.xml
index eb0081ce6..f94a33115 100644
--- a/test/resources/inflection/message2/es_MX.xml
+++ b/test/resources/inflection/message2/es_MX.xml
@@ -8,14 +8,14 @@
         <params>
             <param name="name" type="String"><value>gato</value></param>
         </params>
-        <source>Foo {$name :inflect definiteness=definite number=plural gender=feminine} Bar</source>
+        <source>Foo {$name :i:inflect definiteness=definite number=plural gender=feminine} Bar</source>
         <print>Foo las gatas Bar</print>
     </test>
     <test>
         <params>
             <param name="name" type="String"><value>gato</value></param>
         </params>
-        <source>.local $var1 = {$name :inflect to=gender} .local $var2 = {$name :inflect to=number} .match $var1 $var2
+        <source>.local $var1 = {$name :i:inflect to=gender} .local $var2 = {$name :i:inflect to=number} .match $var1 $var2
 masculine 2 {{{$name} is Masculine &amp; 2}}
 feminine singular {{{$name} is Feminine &amp; Singular}}
 foo 4 {{{$name} is Foo &amp; 4}}
@@ -30,7 +30,7 @@ hello singular {{{$name} is Hello &amp; Singular}}
             <param name="n" type="Number"><value>1</value></param>
             <param name="unit" type="String"><value>niño</value></param>
         </params>
-        <source>Hay {$unit :quantify withValue=$n} en el video</source>
+        <source>Hay {$unit :i:quantify withValue=$n} en el video</source>
         <print>Hay 1 niño en el video</print>
         <speak>Hay un niño en el video</speak>
     </test>
@@ -39,7 +39,7 @@ hello singular {{{$name} is Hello &amp; Singular}}
             <param name="n" type="Number"><value>1</value></param>
             <param name="unit" type="String"><value>niña</value></param>
         </params>
-        <source>Hay {$unit :quantify withValue=$n} en el video</source>
+        <source>Hay {$unit :i:quantify withValue=$n} en el video</source>
         <print>Hay 1 niña en el video</print>
         <speak>Hay una niña en el video</speak>
     </test>
@@ -48,7 +48,7 @@ hello singular {{{$name} is Hello &amp; Singular}}
             <param name="n" type="Number"><value>3</value></param>
             <param name="unit" type="String"><value>niño</value></param>
         </params>
-        <source>Hay {$unit :quantify withValue=$n} en el video</source>
+        <source>Hay {$unit :i:quantify withValue=$n} en el video</source>
         <print>Hay 3 niños en el video</print>
         <speak>Hay tres niños en el video</speak>
     </test>
@@ -56,56 +56,56 @@ hello singular {{{$name} is Hello &amp; Singular}}
         <params>
             <param name="words" type="String[]"><value>gato</value><value>gata</value><value>gatos</value><value>gatas</value></param>
         </params>
-        <source>¿Te gustan los videos sobre {$words :list withType=and definiteness=definite}?</source>
+        <source>¿Te gustan los videos sobre {$words :i:list withType=and definiteness=definite}?</source>
         <print>¿Te gustan los videos sobre el gato, la gata, los gatos y las gatas?</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gatos</value></param>
         </params>
-        <source>¿Te gustan los videos sobre {$words :list withType=and definiteness=definite}?</source>
+        <source>¿Te gustan los videos sobre {$words :i:list withType=and definiteness=definite}?</source>
         <print>¿Te gustan los videos sobre los gatos?</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gatos</value><value>idiomas</value></param>
         </params>
-        <source>¿Te gustan los videos sobre {$words :list withType=and}?</source>
+        <source>¿Te gustan los videos sobre {$words :i:list withType=and}?</source>
         <print>¿Te gustan los videos sobre gatos e idiomas?</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>idiomas</value><value>gatos</value></param>
         </params>
-        <source>¿Te gustan los videos sobre {$words :list withType=and}?</source>
+        <source>¿Te gustan los videos sobre {$words :i:list withType=and}?</source>
         <print>¿Te gustan los videos sobre idiomas y gatos?</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gatos</value><value>idiomas</value></param>
         </params>
-        <source>¿Te gustan los videos sobre {$words :list withType=or}?</source>
+        <source>¿Te gustan los videos sobre {$words :i:list withType=or}?</source>
         <print>¿Te gustan los videos sobre gatos o idiomas?</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gatos</value><value>idiomas</value></param>
         </params>
-        <source>{$words :list}</source>
+        <source>{$words :i:list}</source>
         <print>gatosidiomas</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gato</value><value>gata</value><value>gatos</value></param>
         </params>
-        <source>{$words :list withItemDelimiter=|, | withBeforeLast=| y | withItemPrefix=|[| withItemSuffix=|]|}</source>
+        <source>{$words :i:list withItemDelimiter=|, | withBeforeLast=| y | withItemPrefix=|[| withItemSuffix=|]|}</source>
         <print>[gato], [gata] y [gatos]</print>
     </test>
     <test>
         <params>
             <param name="words" type="String[]"><value>gato</value><value>gata</value></param>
         </params>
-        <source>{$words :list withType=and withAvoidItemAffixRedundancy=false}</source>
+        <source>{$words :i:list withType=and withAvoidItemAffixRedundancy=false}</source>
         <print>gato y gata</print>
     </test>
     <test>
@@ -113,7 +113,7 @@ hello singular {{{$name} is Hello &amp; Singular}}
             <param name="p" type="String"><value>mío</value></param>
             <param name="obj" type="String"><value>casas</value></param>
         </params>
-        <source>{$p :pronoun withReferent=$obj}</source>
+        <source>{$p :i:pronoun withReferent=$obj}</source>
         <print>mías</print>
     </test>
 </message2test>
diff --git a/test/resources/inflection/message2/ru_RU.xml b/test/resources/inflection/message2/ru_RU.xml
index d8053abd2..eca573164 100644
--- a/test/resources/inflection/message2/ru_RU.xml
+++ b/test/resources/inflection/message2/ru_RU.xml
@@ -9,7 +9,7 @@
             <param name="n" type="Number"><value>1</value></param>
             <param name="unit" type="String"><value>километр</value></param>
         </params>
-        <source>{$unit :quantify withValue=$n} {$unit :quantify withValue=$n case=genitive} {$unit :quantify withValue=$n case=accusative} {$unit :quantify withValue=$n case=dative} {$unit :quantify withValue=$n case=instrumental} {$unit :quantify withValue=$n case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$n} {$unit :i:quantify withValue=$n case=genitive} {$unit :i:quantify withValue=$n case=accusative} {$unit :i:quantify withValue=$n case=dative} {$unit :i:quantify withValue=$n case=instrumental} {$unit :i:quantify withValue=$n case=prepositional}</source>
         <print>1 километр 1 километра 1 километр 1 километру 1 километром 1 километре</print>
     </test>
     <test>
@@ -17,7 +17,7 @@
             <param name="n" type="Number"><value>2</value></param>
             <param name="unit" type="String"><value>километр</value></param>
         </params>
-        <source>{$unit :quantify withValue=$n} {$unit :quantify withValue=$n case=genitive} {$unit :quantify withValue=$n case=accusative} {$unit :quantify withValue=$n case=dative} {$unit :quantify withValue=$n case=instrumental} {$unit :quantify withValue=$n case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$n} {$unit :i:quantify withValue=$n case=genitive} {$unit :i:quantify withValue=$n case=accusative} {$unit :i:quantify withValue=$n case=dative} {$unit :i:quantify withValue=$n case=instrumental} {$unit :i:quantify withValue=$n case=prepositional}</source>
         <print>2 километра 2 километров 2 километра 2 километрам 2 километрами 2 километрах</print>
     </test>
     <test>
@@ -25,7 +25,7 @@
             <param name="n" type="Number"><value>5</value></param>
             <param name="unit" type="String"><value>километр</value></param>
         </params>
-        <source>{$unit :quantify withValue=$n} {$unit :quantify withValue=$n case=genitive} {$unit :quantify withValue=$n case=accusative} {$unit :quantify withValue=$n case=dative} {$unit :quantify withValue=$n case=instrumental} {$unit :quantify withValue=$n case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$n} {$unit :i:quantify withValue=$n case=genitive} {$unit :i:quantify withValue=$n case=accusative} {$unit :i:quantify withValue=$n case=dative} {$unit :i:quantify withValue=$n case=instrumental} {$unit :i:quantify withValue=$n case=prepositional}</source>
         <print>5 километров 5 километров 5 километров 5 километрам 5 километрами 5 километрах</print>
     </test>
     <test>
@@ -45,7 +45,7 @@
                 <value constraint="neuter prepositional plural">prepositional,plural</value>
             </param>
         </params>
-        <source>{$unit :inflect gender=neuter case=genitive number=singular}</source>
+        <source>{$unit :i:inflect gender=neuter case=genitive number=singular}</source>
         <print>genitive,singular</print>
     </test>
     <test>
@@ -66,7 +66,7 @@
                 <value constraint="neuter prepositional plural">prepositional,plural</value>
             </param>
         </params>
-        <source>{$unit :quantify withValue=$number} {$unit :quantify withValue=$number case=genitive} {$unit :quantify withValue=$number case=accusative} {$unit :quantify withValue=$number case=dative} {$unit :quantify withValue=$number case=instrumental} {$unit :quantify withValue=$number case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$number} {$unit :i:quantify withValue=$number case=genitive} {$unit :i:quantify withValue=$number case=accusative} {$unit :i:quantify withValue=$number case=dative} {$unit :i:quantify withValue=$number case=instrumental} {$unit :i:quantify withValue=$number case=prepositional}</source>
         <print>1 nominative,singular 1 genitive,singular 1 accusative,singular 1 dative,singular 1 instrumental,singular 1 prepositional,singular</print>
         <speak>одно nominative,singular одного genitive,singular одно accusative,singular одному dative,singular одним instrumental,singular одном prepositional,singular</speak>
     </test>
@@ -88,7 +88,7 @@
                 <value constraint="neuter prepositional plural">prepositional,plural</value>
             </param>
         </params>
-        <source>{$unit :quantify withValue=$number} {$unit :quantify withValue=$number case=genitive} {$unit :quantify withValue=$number case=accusative} {$unit :quantify withValue=$number case=dative} {$unit :quantify withValue=$number case=instrumental} {$unit :quantify withValue=$number case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$number} {$unit :i:quantify withValue=$number case=genitive} {$unit :i:quantify withValue=$number case=accusative} {$unit :i:quantify withValue=$number case=dative} {$unit :i:quantify withValue=$number case=instrumental} {$unit :i:quantify withValue=$number case=prepositional}</source>
         <print>2 genitive,singular 2 genitive,plural 2 genitive,plural 2 dative,plural 2 instrumental,plural 2 prepositional,plural</print>
         <speak>два genitive,singular двух genitive,plural два genitive,plural двум dative,plural двумя instrumental,plural двух prepositional,plural</speak>
     </test>
@@ -110,7 +110,7 @@
                 <value constraint="neuter prepositional plural">prepositional,plural</value>
             </param>
         </params>
-        <source>{$unit :quantify withValue=$number} {$unit :quantify withValue=$number case=genitive} {$unit :quantify withValue=$number case=accusative} {$unit :quantify withValue=$number case=dative} {$unit :quantify withValue=$number case=instrumental} {$unit :quantify withValue=$number case=prepositional}</source>
+        <source>{$unit :i:quantify withValue=$number} {$unit :i:quantify withValue=$number case=genitive} {$unit :i:quantify withValue=$number case=accusative} {$unit :i:quantify withValue=$number case=dative} {$unit :i:quantify withValue=$number case=instrumental} {$unit :i:quantify withValue=$number case=prepositional}</source>
         <print>5 genitive,plural 5 genitive,plural 5 genitive,plural 5 dative,plural 5 instrumental,plural 5 prepositional,plural</print>
         <speak>пять genitive,plural пяти genitive,plural пять genitive,plural пяти dative,plural пятью instrumental,plural пяти prepositional,plural</speak>
     </test>
@@ -131,7 +131,7 @@
                 <value constraint="neuter prepositional plural">prepositional,plural</value>
             </param>
         </params>
-        <source>.local $v = {$unit :inflect gender=neuter case=genitive number=singular} .match $v
+        <source>.local $v = {$unit :i:inflect gender=neuter case=genitive number=singular} .match $v
 |genitive,singular| {{matched genitive singular}}
 * {{other}}
 </source>
diff --git a/test/src/inflection/message2/Message2Test.cpp b/test/src/inflection/message2/Message2Test.cpp
index e13ab8388..6b47320e2 100644
--- a/test/src/inflection/message2/Message2Test.cpp
+++ b/test/src/inflection/message2/Message2Test.cpp
@@ -275,13 +275,13 @@ TEST_CASE("Message2Test#testLocales")
     auto buildRegistry = [&](inflection::message2::MF2Factory::OutputMode mode) {
         UErrorCode ec = U_ZERO_ERROR;
         auto r = MFFunctionRegistry::Builder(ec)
-            .adoptFormatter(FunctionName("inflect"), inflection::message2::MF2Factory::createInflectFormatterFactory(mode), ec)
-            .adoptSelector(FunctionName("inflect"), inflection::message2::MF2Factory::createInflectSelectorFactory(), ec)
-            .adoptFormatter(FunctionName("numeral"), inflection::message2::MF2Factory::createNumeralFormatterFactory(mode), ec)
-            .adoptFormatter(FunctionName("quantify"), inflection::message2::MF2Factory::createQuantifyFormatterFactory(mode), ec)
-            .adoptFormatter(FunctionName("list"), inflection::message2::MF2Factory::createListFormatterFactory(mode), ec)
-            .adoptFormatter(FunctionName("pronoun"), inflection::message2::MF2Factory::createPronounFormatterFactory(mode), ec)
-            .adoptSelector(FunctionName("pronoun"), inflection::message2::MF2Factory::createPronounSelectorFactory(), ec)
+            .adoptFormatter(FunctionName("i:inflect"), inflection::message2::MF2Factory::createInflectFormatterFactory(mode), ec)
+            .adoptSelector(FunctionName("i:inflect"), inflection::message2::MF2Factory::createInflectSelectorFactory(), ec)
+            .adoptFormatter(FunctionName("i:numeral"), inflection::message2::MF2Factory::createNumeralFormatterFactory(mode), ec)
+            .adoptFormatter(FunctionName("i:quantify"), inflection::message2::MF2Factory::createQuantifyFormatterFactory(mode), ec)
+            .adoptFormatter(FunctionName("i:list"), inflection::message2::MF2Factory::createListFormatterFactory(mode), ec)
+            .adoptFormatter(FunctionName("i:pronoun"), inflection::message2::MF2Factory::createPronounFormatterFactory(mode), ec)
+            .adoptSelector(FunctionName("i:pronoun"), inflection::message2::MF2Factory::createPronounSelectorFactory(), ec)
             .build();
         REQUIRE(U_SUCCESS(ec));
         return r;
@@ -414,7 +414,7 @@ TEST_CASE("Message2Test#testLocales")
                 .setLocale(icuLocale)
                 .setPattern(UnicodeString(source.c_str()), pe, testError);
             if (errorExpected) {
-                // Surface MF errors (e.g. an unknown :inflect feature) via the UErrorCode.
+                // Surface MF errors (e.g. an unknown :i:inflect feature) via the UErrorCode.
                 builder.setErrorHandlingBehavior(MessageFormatter::U_MF_STRICT);
             }
             MessageFormatter mf = builder.build(testError);