Based on your sample:
Raw Match Pattern:
<span class="myClass">(.*?)</span>\r\n(.*?)(?:\r|$)
PHP Code Example:
<?php
$sourcestring="your source string";
preg_match_all('#<span class="myClass">(.*?)</span>\r\n(.*?)(?:\r|$)#',$sourcestring,$matches);
echo "<pre>".print_r($matches,true);
?>
$matches Array:
(
[0] => Array
(
[0] => <span class="myClass">some text 1</span>
some text under 1
[1] => <span class="myClass">some text 2</span>
some text under 2
[2] => <span class="myClass">some text 3</span>
some text under 3
)
[1] => Array
(
[0] => some text 1
[1] => some text 2
[2] => some text 3
)
[2] => Array
(
[0] => some text under 1
[1] => some text under 2
[2] => some text under 3
)
)