my $s = ...;

my $t = $s;
utf8::upgrade( $t );

say utf8::is_utf8( $t ) ?1:0;   # 1
say $s eq $t            ?1:0;   # 1

##</code><code>##

my $s = ...;

my $t = $s;
utf8::downgrade( $t );          # Might croak

say utf8::is_utf8( $t ) ?1:0;   # 0
say $s eq $t            ?1:0;   # 1

##</code><code>##

utf8::decode( $_ ) if !utf8::is_utf8( $_ );

##</code><code>##

utf8::encode( $_ ) if utf8::is_utf8( $_ );