Index: wp-admin/js/editor.dev.js
===================================================================
--- wp-admin/js/editor.dev.js	(revision 21212)
+++ wp-admin/js/editor.dev.js	(working copy)
@@ -7,7 +7,7 @@
 		this.go(id, mode);
 	},
 
-	go: function(id, mode) { // mode can be 'html', 'tmce', or 'toggle'
+	go: function(id, mode) { // mode can be 'html', 'tmce', or 'toggle'; 'html' is used for the "Text" editor tab (Quicktags)
 		id = id || 'content';
 		mode = mode || 'toggle';
 
Index: wp-includes/class-wp-editor.php
===================================================================
--- wp-includes/class-wp-editor.php	(revision 21212)
+++ wp-includes/class-wp-editor.php	(working copy)
@@ -76,6 +76,7 @@
 		if ( self::$this_quicktags && self::$this_tinymce ) {
 			$switch_class = 'html-active';
 
+			// 'html' and 'switch-html' are used for the "Text" editor tab (Quicktags)
 			if ( 'html' == wp_default_editor() ) {
 				add_filter('the_editor_content', 'wp_htmledit_pre');
 			} else {
Index: wp-includes/general-template.php
===================================================================
--- wp-includes/general-template.php	(revision 21212)
+++ wp-includes/general-template.php	(working copy)
@@ -1767,7 +1767,7 @@
  * Find out which editor should be displayed by default.
  *
  * Works out which of the two editors to display as the current editor for a
- * user.
+ * user. The 'html' setting is for the "Text" editor tab (Quicktags).
  *
  * @since 2.5.0
  *