Introduce 'rss_tag_pre' action, which fires between the xml and rss tags in a feed.

props solarissmoke, wonderboymusic, DrewAPicture.
fixes #19017.
Built from https://develop.svn.wordpress.org/trunk@29014


git-svn-id: http://core.svn.wordpress.org/trunk@28802 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/feed-atom-comments.php

@@ -7,6 +7,9 @@
 
 header('Content-Type: ' . feed_content_type('atom') . '; charset=' . get_option('blog_charset'), true);
 echo '<?xml version="1.0" encoding="' . get_option('blog_charset') . '" ?' . '>';
+
+/** This action is documented in wp-includes/feed-rss2.php */
+do_action( 'rss_tag_pre', 'atom-comments' );
 ?>
 <feed
 	xmlns="http://www.w3.org/2005/Atom"

wp-includes/feed-atom.php

@@ -8,7 +8,11 @@
 header('Content-Type: ' . feed_content_type('atom') . '; charset=' . get_option('blog_charset'), true);
 $more = 1;
 
-echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>'; ?>
+echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>';
+
+/** This action is documented in wp-includes/feed-rss2.php */
+do_action( 'rss_tag_pre', 'atom' );
+?>
 <feed
   xmlns="http://www.w3.org/2005/Atom"
   xmlns:thr="http://purl.org/syndication/thread/1.0"

wp-includes/feed-rdf.php

@@ -8,7 +8,11 @@
 header('Content-Type: ' . feed_content_type('rdf') . '; charset=' . get_option('blog_charset'), true);
 $more = 1;
 
-echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>'; ?>
+echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>';
+
+/** This action is documented in wp-includes/feed-rss2.php */
+do_action( 'rss_tag_pre', 'rdf' );
+?>
 <rdf:RDF
 	xmlns="http://purl.org/rss/1.0/"
 	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

wp-includes/feed-rss2-comments.php

@@ -8,6 +8,9 @@
 header('Content-Type: ' . feed_content_type('rss-http') . '; charset=' . get_option('blog_charset'), true);
 
 echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>';
+
+/** This action is documented in wp-includes/feed-rss2.php */
+do_action( 'rss_tag_pre', 'rss2-comments' );
 ?>
 <rss version="2.0"
 	xmlns:content="http://purl.org/rss/1.0/modules/content/"

wp-includes/feed-rss2.php

@@ -8,8 +8,18 @@
 header('Content-Type: ' . feed_content_type('rss-http') . '; charset=' . get_option('blog_charset'), true);
 $more = 1;
 
-echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>'; ?>
+echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>';
 
+/**
+ * Fires between the <xml> and <rss> tags in a feed.
+ *
+ * @since 4.0.0
+ *
+ * @param string $context Type of feed. Possible values include 'rss2', 'rss2-comments',
+ *                        'rdf', 'atom', and 'atom-comments'.
+ */
+do_action( 'rss_tag_pre', 'rss2' );
+?>
 <rss version="2.0"
 	xmlns:content="http://purl.org/rss/1.0/modules/content/"
 	xmlns:wfw="http://wellformedweb.org/CommentAPI/"