Implement XMLSERIALIZE for real. Analogously, make the xml to text cast

observe the xmloption.

Reorganize the representation of the XML option in the parse tree and the
API to make it easier to manage and understand.

Add regression tests for parsing back XML expressions.

src/include/nodes/primnodes.h

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.123 2007/01/14 13:11:54 petere Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.124 2007/02/03 14:06:56 petere Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -726,9 +726,16 @@ typedef enum XmlExprOp
 	IS_XMLPARSE,				/* XMLPARSE(text, is_doc, preserve_ws) */
 	IS_XMLPI,					/* XMLPI(name [, args]) */
 	IS_XMLROOT,					/* XMLROOT(xml, version, standalone) */
+	IS_XMLSERIALIZE,			/* XMLSERIALIZE(is_document, xmlval) */
 	IS_DOCUMENT					/* xmlval IS DOCUMENT */
 } XmlExprOp;
 
+typedef enum
+{
+	XMLOPTION_DOCUMENT,
+	XMLOPTION_CONTENT
+} XmlOptionType;
+
 typedef struct XmlExpr
 {
 	Expr		xpr;
@@ -737,6 +744,9 @@ typedef struct XmlExpr
 	List	   *named_args;		/* non-XML expressions for xml_attributes */
 	List	   *arg_names;		/* parallel list of Value strings */
 	List	   *args;			/* list of expressions */
+	XmlOptionType xmloption;	/* DOCUMENT or CONTENT */
+	Oid			type;			/* target type for XMLSERIALIZE */
+	int32		typmod;
 } XmlExpr;
 
 /*