Index: pyyaml/trunk/lib/yaml/emitter.py
===================================================================
--- pyyaml/trunk/lib/yaml/emitter.py	(revision 308)
+++ pyyaml/trunk/lib/yaml/emitter.py	(revision 313)
@@ -77,4 +77,7 @@
         self.indention = True
 
+        # Whether the document requires an explicit document indicator
+        self.open_ended = False
+
         # Formatting details.
         self.canonical = canonical
@@ -170,4 +173,7 @@
     def expect_document_start(self, first=False):
         if isinstance(self.event, DocumentStartEvent):
+            if (self.event.version or self.event.tags) and self.open_ended:
+                self.write_indicator(u'...', True)
+                self.write_indent()
             if self.event.version:
                 version_text = self.prepare_version(self.event.version)
@@ -193,4 +199,7 @@
             self.state = self.expect_document_root
         elif isinstance(self.event, StreamEndEvent):
+            if self.open_ended:
+                self.write_indicator(u'...', True)
+                self.write_indent()
             self.write_stream_end()
             self.state = self.expect_nothing
@@ -793,4 +802,5 @@
         self.indention = self.indention and indention
         self.column += len(data)
+        self.open_ended = False
         if self.encoding:
             data = data.encode(self.encoding)
@@ -977,4 +987,6 @@
         hints = self.determine_block_hints(text)
         self.write_indicator(u'>'+hints, True)
+        if hints[-1:] == u'+':
+            self.open_ended = True
         self.write_line_break()
         leading_space = True
@@ -1026,6 +1038,8 @@
 
     def write_literal(self, text):
-        chomp = self.determine_block_hints(text)
-        self.write_indicator(u'|'+chomp, True)
+        hints = self.determine_block_hints(text)
+        self.write_indicator(u'|'+hints, True)
+        if hints[-1:] == u'+':
+            self.open_ended = True
         self.write_line_break()
         breaks = True
@@ -1059,4 +1073,6 @@
 
     def write_plain(self, text, split=True):
+        if self.root_context:
+            self.open_ended = True
         if not text:
             return