As this is XML, it also makes sense to use some sort of XML parser, which is more flexible. For example: (code is tested)

use XML::Simple;
use Data::Dumper;
use strict;

my $parser = new XML::Simple();
my $ref = $parser->XMLin("<xml>".'<span class="style">28.56</span><spa
+n class="style">-1.22</span><span class="style">-4.1</span><span clas
+s="style">04/02</span>'."</xml>");
print $ref->{span}[0]{content}, "\n";
print $ref->{span}[1]{content};
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If your string could be long, then use some parser that does not slurp.