Improve XML serialization, URI parsing, and XPath node set processing.

third_party/libxml/src/parser.c

Index: third_party/libxml/src/parser.c
diff --git a/third_party/libxml/src/parser.c b/third_party/libxml/src/parser.c
index 745c3da1c72e11a896c6da1269a1cd7172c71242..c300788247c323529d766155963f6470d7135bcb 100644
--- a/third_party/libxml/src/parser.c
+++ b/third_party/libxml/src/parser.c
@@ -8147,6 +8147,14 @@ xmlParsePEReference(xmlParserCtxtPtr ctxt)
 	    if (xmlPushInput(ctxt, input) < 0)
 		return;
 	} else {
+	    if ((entity->etype == XML_EXTERNAL_PARAMETER_ENTITY) &&
+	        ((ctxt->options & XML_PARSE_NOENT) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDVALID) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDLOAD) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDATTR) == 0) &&
+	        (ctxt->replaceEntities == 0) &&
+	        (ctxt->validate == 0))
+	        return;
 	    /*
 	     * TODO !!!
 	     * handle the extra spaces added before and after