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/**
 * At the end of every blockquote, include a link to tweet the quote
 *
 * @param $content
 *
 * @return mixed
 */
 function myprefix_add_twitter_link_to_blockquote( $content ) {

	$content = preg_replace( '#(<blockquote><p>)(.*)(</p></blockquote>)#m', '$1 $2 <a href="http://twitter.com/intent/tweet?status=$2 via @twitterusername ' . get_the_permalink() . '" class="genericon genericon-twitter" target="_blank">Tweet This</a> $3', $content );
	return $content;

}
add_filter( 'the_content', 'myprefix_add_twitter_link_to_blockquote' );