diff --git a/source/dom_persist.d b/source/dom_persist.d
index ead40bf..bcb8b2c 100644
--- a/source/dom_persist.d
+++ b/source/dom_persist.d
@@ -12,20 +12,32 @@
 
 import nodecode;
 
-import d2sqlite3;	// https://d2sqlite3.dpldocs.info/v1.0.0/d2sqlite3.database.Database.this.html
-						// https://dlang-community.github.io/d2sqlite3/d2sqlite3.html
+// https://d2sqlite3.dpldocs.info/v1.0.0/d2sqlite3.database.Database.this.html
+// https://d2sqlite3.dpldocs.info/v1.0.0/source/tests.d.d.html
+// https://dlang-community.github.io/d2sqlite3/d2sqlite3.html
+// https://code.dlang.org/packages/d2sqlite3
+import d2sqlite3;	
 
 
+/**
+ * Return true if the database exists.
+ */
 bool db_exists( string sqlite_filename ){
 	return sqlite_filename.exists;
 }
 
+/**
+ * Drop the database and remove the DB file
+ */
 void db_drop( string sqlite_filename ){
 	if( sqlite_filename.exists ){
 		sqlite_filename.remove();
 	}	
 }
 
+/**
+ * Create the database file and the params table with the DB version number.
+ */
 Database db_create( string sqlite_filename, int db_ver ){
 	
 	auto db = Database( sqlite_filename );
@@ -35,82 +47,19 @@
 }
 
 
-string get_openTag_commence( TreeNodeType nt, string e_data ){
-	
-	switch( nt ){
-	
-	case TreeNodeType.text:
-		return e_data;
-		
-	case TreeNodeType.comment:
-		return "<!--"~e_data;
-		
-	case TreeNodeType.docType:
-		return "<DOCTYPE "~e_data;
-
-	default:
-		return "<"~e_data;
-	}
-}
-
-string get_openTag_end( TreeNodeType nt, string e_data ){
-
-	switch( nt ){
-		
-	case TreeNodeType.comment:
-	case TreeNodeType.text:
-		return "";
-			
-	default:
-		switch(e_data){
-		case "input":
-		case "br":
-			return "/>";
-		default:
-		}
-		
-		return ">";
-	}
-	
-}
-
-string get_closeTag( TreeNodeType nt, string e_data ){
-
-	switch( nt ){
-		
-	case TreeNodeType.docType:
-	case TreeNodeType.text:
-		return "";
-		
-	case TreeNodeType.comment:
-		return "-->";
-		
-	default:
-		switch(e_data){
-		case "input":
-		case "br":
-			return "";
-		default:
-		}
-
-		return format("</%s>", e_data);
-	}
-	
-}
 
 struct TreeNameID {
 	long tree_id;
 	string name;
 }
 
-
 /**
  * An instance of this class contains access to a single tree. Tree operations are cached in RAM and only written to
- * disk during a save operation. This can be done safely because of the single user access to Sqlite.
+ * disk when flush is called. This can be done safely because of the single user access to Sqlite.
  * 
- * Multiple database connections should work on the same thread provided each is using a different tree.
+ * Multiple database connections have not been tested. 
+ * Multiple threads not yet supported.
  * 
- * Instantiation of the tree involves only one database select.
  */
 class Tree_Db {
 
@@ -176,6 +125,9 @@
 
 	public:
 	
+	/**
+	 * Create the Database schema for the trees.
+	 */
 	static void db_create_schema( ref Database db ){		
 		db.run("CREATE TABLE IF NOT EXISTS doctree (ID INTEGER, e_data	TEXT,p_id INTEGER,t_id INTEGER NOT NULL,tree_id INTEGER NOT NULL,	c_order INTEGER, PRIMARY KEY( ID AUTOINCREMENT))");
 	}
@@ -205,7 +157,7 @@
 	}
 
 	/**
-	 * Load a tree into RAM from database given the tree ID.
+	 * Load a tree into RAM from database given the tree ID. Reads the complete tree and involves only one database select.
 	 */
 	static Tree_Db loadTree( ref Database db, long tree_id ){
 		return new Tree_Db( &db, tree_id );		
@@ -437,6 +389,68 @@
 	
 }
 
+private string get_openTag_commence( TreeNodeType nt, string e_data ){
+	
+	switch( nt ){
+	
+	case TreeNodeType.text:
+		return e_data;
+		
+	case TreeNodeType.comment:
+		return "<!--"~e_data;
+		
+	case TreeNodeType.docType:
+		return "<DOCTYPE "~e_data;
+
+	default:
+		return "<"~e_data;
+	}
+}
+
+private string get_openTag_end( TreeNodeType nt, string e_data ){
+
+	switch( nt ){
+		
+	case TreeNodeType.comment:
+	case TreeNodeType.text:
+		return "";
+			
+	default:
+		switch(e_data){
+		case "input":
+		case "br":
+			return "/>";
+		default:
+		}
+		
+		return ">";
+	}
+	
+}
+
+private string get_closeTag( TreeNodeType nt, string e_data ){
+
+	switch( nt ){
+		
+	case TreeNodeType.docType:
+	case TreeNodeType.text:
+		return "";
+		
+	case TreeNodeType.comment:
+		return "-->";
+		
+	default:
+		switch(e_data){
+		case "input":
+		case "br":
+			return "";
+		default:
+		}
+
+		return format("</%s>", e_data);
+	}
+	
+}
 
 /**
  * Iterator starting at any given TreeNode, traversing each of the descendent nodes, depth first and increasing child index.
diff --git a/source/nodecode.d b/source/nodecode.d
index 022cdb1..422b2f1 100644
--- a/source/nodecode.d
+++ b/source/nodecode.d
@@ -20,15 +20,16 @@
 	return TreeNodeType.nulltype;
 }
 
-
+/**
+ * Node data held by each TreeNode.
+ */
 struct NodeData {
 	
-	long ID;
-	string e_data;
-	long pid;
+	long ID;			// The (database) ID of this node. negative IDs are new nodes not yet flushed
+	string e_data;	// Data specific to the node. e.g. element name, or comment text etc..
+	long pid;		// Parent node ID. If not connected then zero
 	TreeNodeType type;
-	bool dirty = false;
-	long orig_pid=0;
+	bool dirty = false;	// true when any node data changes indicating a DB write is required.	
 	
 	this( long ID, string e_data, long pid, TreeNodeType type){
 		this.ID = ID;
@@ -39,14 +40,9 @@
 }
 
 /**
- * TreeNode is a class because we need the references to remain valid when we modify containers such as
- * the hashmap which indexes on ID.
+ * Each element in the tree is represented by an instance of TreeNode.
  * 
- * If we use a struct, then we need to hold the TreeNode data somewhere in order to use a pointer to the data. If
- * we move the data, such as updating a map, then all the pointers need to change, or we need pointers to pointers.
- * Either is not ideal. If we use references, as provided by a class, then the GC will track the references and ensure
- * that they remain valid. We can move the references knowing that the data remains in place on the heap
- * 
+ * This class contains node specific operations such as reading, mutation, relocation etc..
  */
 class TreeNode {
 	
@@ -155,14 +151,16 @@
 		}
 	
 		/**
-		 * Delete this node from the the tree.
+		 * Delete this node and all it's descendents from the the tree.
 		 */
 		void deleteNode( ){
 			owner_tree.deleteNode( this );
 		}
 
 		/**
-		 * Internal use only
+		 * Internal use only.
+		 * 
+		 * Locate the child node (c_node) and snip it off.
 		 */
 		void cutChild( TreeNode c_node ){
 			foreach( i, child; child_nodes ){