$re = '/([^. >"])([ ])?([-])?(<\/p>)\n.*?>/';
$str = '<p class="calibre1">pelled itself, riderless, in an endless orbit. </p>
<p class="calibre1">The generator complex on the far side of this battlefield was </p>
<p class="calibre1">intact, however. Reinforced concrete bunkers bristling with ma-</p>
<p class="calibre1">chine guns surrounded a low building. The generators were deep </p>
<p class="calibre1">beneath there. So far it looked as if the Covenant had not man-</p>
<p class="calibre1">aged to take them, though not for lack of trying. </p>
<p class="calibre1">"Contacts ahead," Joshua whispered. </p>
<p class="calibre1">Four blips appeared on his motion sensor. Friend-or-foe tags </p>
<p class="calibre1">identified them as UNSC Marines, Company Charlie. Serial </p>
<p class="calibre1">numbers flashed next to the men as his HUD picked them out on a </p>
<p class="calibre1">topo map of the area. </p>
<p class="calibre1">Joshua handed Fred his sniper rifle, and he sighted the con-</p>
<p class="calibre1">tacts through the scope. They were Marines, sure enough. They </p>
<p class="calibre1">picked through the bodies that littered the area, looking for sur-</p>
<p class="calibre1">vivors and policing weapons and ammo. </p>
<p class="calibre1">Fred frowned; something about the way the Marine squad </p>
<p class="calibre1">moved didn\'t feel right. They lacked unit cohesion, with their </p>
<p class="calibre1">firstd, <i class="calibre4">you may as well drop with good intel. </i> </p>
<p class="calibre1">Captain Keyes frowned on the ship\'s viewscreen, a </p>
<p class="calibre1">"Roger that," he replied, "though I think I\'ve had enough surprises for one op." </p>
<p class="calibre1">Kelly chuckled. </p>';
$subst = "$1$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php