Index :api and add bit of documentation

refs: #3308

Author: uzluisf

doc/Language/typesystem.pod6

@@ -536,17 +536,21 @@ attributes is not yet implemented. Please note that adding a multi candidate
 that differs only in its named parameters will add that candidate behind the
 already defined one and as such it won't be picked by the dispatcher.
 
-=head3 Versioning and authorship
-
-Versioning and authorship can be applied via the adverbs
-X«C«:ver<>»|:ver<> (class)» and X«C«:auth<>»|:auth<> (class)».
-Both take a string as argument, for C<:ver> the string is converted to a
-L<Version|/type/Version> object. To query a class version and author use
-C<.^ver> and C<^.auth>.
-
-    class C:ver<4.2.3>:auth<me@here.local> {}
-    say [C.^ver, C.^auth];
-    # OUTPUT: «[v4.2.3 me@here.local]␤»
+=head3 Versioning, authorship, and API
+
+Versioning, authorship, and API can be applied via the adverbs
+X«C«:ver<>»|:ver<> (class)», X«C«:auth<>»|:auth<> (class)», and
+X«C«:api<>»|:api<> (class)» respectively. All of them take a string as argument;
+for C<:ver> the string is converted to a L<Version|/type/Version> object,
+and for C<:api> the string is converted into the allomorph
+L«C«IntStr»|/type/IntStr». To query a class about its version, author, and API
+use C<.^ver>, C<.^auth>, and C<.^api> respectively.
+
+    class C:ver<4.2.3>:auth<me@here.local>:api<1> {}
+    say C.^ver;       # OUTPUT: «v4.2.3␤»
+    say C.^ver.parts; # OUTPUT: «(4 2 3)␤»
+    say C.^auth;      # OUTPUT: «me@here.local␤»
+    say C.^api;       # OUTPUT: «1␤»
 
 =head2 C<role>
 
@@ -686,17 +690,21 @@ say [(75kg).^name, N(75kg).^name];
 # OUTPUT: «[Int+{SI-kilogram} Rat+{SI-Newton}]␤»
 =end code
 
-=head3 Versioning and authorship
+=head3 Versioning, authorship, and API
 
-Versioning and authorship can be applied via the adverbs
-X«C«:ver<>»|:ver<> (role)» and X«C«:auth<>»|:auth<> (role)».
-Both take a string as argument, for C<:ver> the string is converted to a
-L<Version|/type/Version> object. To query a role's version and author use
-C<.^ver> and C<^.auth>.
+Versioning, authorship, and API can be applied via the adverbs
+X«C«:ver<>»|:ver<> (role)», X«C«:auth<>»|:auth<> (role)», and
+X«C«:api<>»|:api<> (role)» respectively. All of them take a string as argument;
+for C<:ver> the string is converted to a L<Version|/type/Version> object,
+and for C<:api> the string is converted into the allomorph
+L«C«IntStr»|/type/IntStr». To query a role's version, author, and API
+use C<.^ver>, C<.^auth>, and C<.^api> respectively.
 
-    role R:ver<4.2.3>:auth<me@here.local> {}
-    say [R.^ver, R.^auth];
-    # OUTPUT: «[v4.2.3 me@here.local]␤»
+    class R:ver<4.2.3>:auth<me@here.local>:api<1> {}
+    say R.^ver;       # OUTPUT: «v4.2.3␤»
+    say R.^ver.parts; # OUTPUT: «(4 2 3)␤»
+    say R.^auth;      # OUTPUT: «me@here.local␤»
+    say R.^api;       # OUTPUT: «1␤»
 
 X<|Enumeration; Enums; enum>
 =head2 C<enum>
@@ -900,16 +908,20 @@ another Raku program.
 
 For a full explanation see L<Modules|/language/modules>.
 
-=head3 Versioning and authorship
+=head3 Versioning, authorship, and API
 
-Versioning and authorship can be applied via the adverbs C«:ver<>» and C«:auth<>».
-Both take a string as argument, for C<:ver> the string is converted to a
-L<Version|/type/Version> object. To query a modules version and author use
-C<.^ver> and C<^.auth>.
+Versioning, authorship, and API can be applied via the adverbs
+C«:ver<>», C«:auth<>», and C«:api<>» respectively. All of them take a string as
+argument; for C<:ver> the string is converted to a L<Version|/type/Version> object,
+and for C<:api> the string is converted into the allomorph
+L«C«IntStr»|/type/IntStr». To query a module's version, author, and API
+use C<.^ver>, C<.^auth>, and C<.^api> respectively.
 
-    module M:ver<4.2.3>:auth<me@here.local> {}
-    say [M.^ver, M.^auth];
-    # OUTPUT: «[v4.2.3 me@here.local]␤»
+    class M:ver<4.2.3>:auth<me@here.local>:api<1> {}
+    say M.^ver;       # OUTPUT: «v4.2.3␤»
+    say M.^ver.parts; # OUTPUT: «(4 2 3)␤»
+    say M.^auth;      # OUTPUT: «me@here.local␤»
+    say M.^api;       # OUTPUT: «1␤»
 
 =head2 C<package>
 
@@ -926,17 +938,21 @@ are classes.
 
 For a full explanation see L<Grammars|/language/grammars>.
 
-=head3 Versioning and authorship
-
-Versioning and authorship can be applied via the adverbs
-X«C«:ver<>»|:ver<> (grammar)» and X«C«:auth<>»|:auth<> (grammar)».
-Both take a string as argument, for C<:ver> the string is converted to a
-L<Version|/type/Version> object. To query a grammars version and author use
-C<.^ver> and C<^.auth>.
-
-    grammar G:ver<4.2.3>:auth<me@here.local> {}
-    say [G.^ver, G.^auth];
-    # OUTPUT: «[v4.2.3 me@here.local]␤»
+=head3 Versioning, authorship, and API
+
+Versioning, authorship, and API can be applied via the adverbs
+X«C«:ver<>»|:ver<> (grammar)», X«C«:auth<>»|:auth<> (grammar)», and
+X«C«:api<>»|:api<> (grammar)» respectively. All of them take a string as argument;
+for C<:ver> the string is converted to a L<Version|/type/Version> object,
+and for C<:api> the string is converted into the allomorph
+L«C«IntStr»|/type/IntStr». To query a grammar about its version, author, and API
+use C<.^ver>, C<.^auth>, and C<.^api> respectively.
+
+    class G:ver<4.2.3>:auth<me@here.local>:api<1> {}
+    say G.^ver;       # OUTPUT: «v4.2.3␤»
+    say G.^ver.parts; # OUTPUT: «(4 2 3)␤»
+    say G.^auth;      # OUTPUT: «me@here.local␤»
+    say G.^api;       # OUTPUT: «1␤»
 
 =head2 C<subset>