$str = join '' => <DATA>;

@arr = map  { m!(<first>.*?</first>)!si }     # extract first
       grep { m!<content>maps</content>!si }  # filter by content
       $str =~ m!<contentmodel>(.*?)</contentmodel>!gsi;  # split on contentmodel

print @arr;

__DATA__
<pages>
<contentmodel>
<level>5</level>
<first>35</first>
<content>some text</content>
</contentmodel>
<contentmodel>
<level>4</level>
<first>45</first>
<content>some text</content>
</contentmodel>
<contentmodel>
<level>3</level>
<first>25</first>
<content>maps</content>
</contentmodel>
<contentmodel>
<level>2</level>
<first>15</first>
<content>some text</content>
</contentmodel>
</pages>