regex capture group names must use identifier syntax

pod/perldiag.pod

@@ -2867,8 +2867,9 @@ has since been undefined.
 S<<-- HERE> in m/%s/
 
 (F) Group names must follow the rules for perl identifiers, meaning
-they must start with a non-digit word character.  A common cause of
-this error is using (?&0) instead of (?0).  See L<perlre>.
+that ASCII-range ones must start with a non-digit word character.  A
+common cause of this error is using (?&0) instead of (?0).  See
+L<perlre> and L<perldata/Identifier parsing>.
 
 =item ()-group starts with a count
 

pod/perlre.pod

@@ -1198,7 +1198,9 @@ You can dispense with numbers altogether and create named capture groups.
 The notation is C<(?E<lt>I<name>E<gt>...)> to declare and C<\g{I<name>}> to
 reference.  (To be compatible with .Net regular expressions, C<\g{I<name>}> may
 also be written as C<\k{I<name>}>, C<\kE<lt>I<name>E<gt>> or C<\k'I<name>'>.)
-I<name> must not begin with a number, nor contain hyphens.
+I<name> must follow the rules for perl identifiers
+(L<perldata/Identifier parsing>) which means, for example, that they
+can't begin with a number, nor contain hyphens.
 When different groups within the same pattern have the same name, any reference
 to that name assumes the leftmost defined group.  Named groups count in
 absolute and relative numbering, and so can also be referred to by those

regcomp.c

@@ -2532,7 +2532,7 @@ S_reg_scan_name(pTHX_ RExC_state_t *pRExC_state, U32 flags)
         do {
             RExC_parse_advance(advance);
         } while (   RExC_parse < RExC_end
-                 && (advance = isWORDCHAR_utf8_safe( (U8 *) RExC_parse,
+                 && (advance = isIDCONT_utf8_safe( (U8 *) RExC_parse,
                                                      (U8 *) RExC_end)));
     } else {
         RExC_parse_inc_by(1); /* so the <- from the vFAIL is after the offending

t/re/pat.t

@@ -28,7 +28,7 @@ skip_all_without_unicode_tables();
 my $has_locales = locales_enabled('LC_CTYPE');
 my $utf8_locale = find_utf8_ctype_locale();
 
-plan tests => 1296;  # Update this when adding/deleting tests.
+plan tests => 1298;  # Update this when adding/deleting tests.
 
 run_tests() unless caller;
 
@@ -1388,6 +1388,28 @@ EOP
             fresh_perl_like($prog, qr!Group name must start with a non-digit word character!, {},
                         sprintf("'U+%04X not legal IDFirst'", ord($char)));
         }
+
+        foreach my $char (chr(0x2115), chr(0x24B7)) {
+            my $prog = <<"EOP";
+use utf8;;
+no warnings 'utf8';
+print 0 + "abc" =~ qr/(?<a${char}b>abc)/;
+EOP
+            utf8::encode($prog);
+            if ($char =~ /\p{XID_Continue}/) {
+                fresh_perl_is($prog, 1,
+                                {},
+                                sprintf("U+%04X is legal IDCont",
+                                        ord($char)));
+            }
+            else {
+                fresh_perl_like($prog,
+                                qr/Sequence .* not terminated/,
+                                {},
+                                sprintf("U+%04X not legal IDCont",
+                                ord($char)));
+            }
+        }
     }
 
     { # [perl #101710]