I have never found the output of a standard diff to be very enlightening. I'm sure it works well to change files, patch-style, but it isn't very readable for someone simply wanting to see what happened to the text in a side-by-side format.

Plain old diff (in the GNU version) has at least four output formats:

• ed script:

  /tmp>diff foo bar
  1,2c1,2
  < Bla bla. Foo bar baz.
  < Nada nada nada. Nada?
  ---
  > Bla bar. Foo bar baz.
  > Nada na-da nada. Nada?
  4c4
  < bar. Bla. Bar bla.
  ---
  > bar. Bla bar bla.
  [download]

• Unified:

  /tmp>diff -u foo bar
  --- foo 2021-01-31 15:13:16.892239748 +0100
  +++ bar 2021-01-31 15:13:43.403869518 +0100
  @@ -1,6 +1,6 @@
  -Bla bla. Foo bar baz.
  -Nada nada nada. Nada?
  +Bla bar. Foo bar baz.
  +Nada na-da nada. Nada?
   Foo foo foo! Bar. Foo
  -bar. Bla. Bar bla.
  +bar. Bla bar bla.
   Foo bla bla nada bar.
  [download]

• Side by side (also available via sdiff)

  /tmp>diff -y foo bar
  Bla bla. Foo bar baz.                                         | Bla ba
  +r. Foo bar baz.
  Nada nada nada. Nada?                                         | Nada n
  +a-da nada. Nada?
  Foo foo foo! Bar. Foo                                           Foo fo
  +o foo! Bar. Foo
  bar. Bla. Bar bla.                                            | bar. B
  +la bar bla.
  Foo bla bla nada bar.                                           Foo bl
  +a bla nada bar.
  [download]

• rcs

  /tmp>diff -n foo bar
  d1 2
  a2 2
  Bla bar. Foo bar baz.
  Nada na-da nada. Nada?
  d4 1
  a4 1
  bar. Bla bar bla.
  [download]

TortoiseSVN comes with a diff and merge tool called TortoiseMerge that can show changes side by side, highlighting not only changed lines, but also changes within the lines.

Side note:

sub comparator {
my $str1 = shift @_;
#...
my $RE = qq|</span> |;

  traverse_sequences( \@from, \@to,
    {
    # ...
    } );
    
    return ($original, $revised);
    
} #END SUB comparator
[download]

Proper indenting would make the "#END SUB comparator" redundant:

sub comparator 
{
    my $str1 = shift @_;
    #...
    my $RE = qq|</span> |;

    traverse_sequences( \@from, \@to,
        {
            # ...
        }
    );
    
    return ($original, $revised);
}
[download]

Alexander