>perl -wMstrict -le
"my @strings = (
   '<B>foo</ b > <EfG>bar</eFg> \"stuff\" <cD >*&!</ Cd> <x>baz</x>',
   '<b>fee</B> P <b>fie</B> Q <efg>foe</EFG> R <efg>fum</EFG> S',
   '<b>hee</b> W <b>hie</b> X <efg>hoe</efg> Y <efg>hum</efg> Z',
   );
 ;;
 my $ar_keep_tag_content = [ 1, tag_group_regex(qw(b cd)) ];
 my $ar_kill_tag_content = [ 0, tag_group_regex(qw(efg) ) ];
 ;;
 for my $s (@strings) {
   print qq{'$s'};
   for my $pass ($ar_keep_tag_content, $ar_kill_tag_content) {
     my ($keep_content, $tag) = @$pass;
     $s =~ s{ < \s* ($tag) \s* >  (.*?)  </ \s* (?i) \1 \s* > }
            { $keep_content ? $2 : '' }xmsge;
     print qq{'$s'};
     }
     print '';
   }
 ;;
 sub tag_group_regex {
   my $alternation = join '|', @_;
   return qr{ (?i) $alternation }xms;
   }
"
'<B>foo</ b > <EfG>bar</eFg> "stuff" <cD >*&!</ Cd> <x>baz</x>'
'foo <EfG>bar</eFg> "stuff" *&! <x>baz</x>'
'foo  "stuff" *&! <x>baz</x>'

'<b>fee</B> P <b>fie</B> Q <efg>foe</EFG> R <efg>fum</EFG> S'
'fee P fie Q <efg>foe</EFG> R <efg>fum</EFG> S'
'fee P fie Q  R  S'

'<b>hee</b> W <b>hie</b> X <efg>hoe</efg> Y <efg>hum</efg> Z'
'hee W hie X <efg>hoe</efg> Y <efg>hum</efg> Z'
'hee W hie X  Y  Z'