Index: branches/pyyaml3000/lib/yaml/error.py
===================================================================
--- branches/pyyaml3000/lib/yaml/error.py	(revision 45)
+++ branches/pyyaml3000/lib/yaml/error.py	(revision 52)
@@ -1,4 +1,79 @@
+
+__all__ = ['Marker', 'YAMLError', 'MarkedYAMLError']
+
+class Marker:
+
+    def __init__(self, name, line, column, buffer, pointer):
+        self.name = name
+        self.line = line
+        self.column = column
+        self.buffer = buffer
+        self.pointer = pointer
+
+    def get_snippet(self, indent=4, max_length=75):
+        if self.buffer is None:
+            return None
+        head = ''
+        start = self.pointer
+        while start > 0 and self.buffer[start-1] not in u'\0\r\n\x85\u2028\u2029':
+            start -= 1
+            if self.pointer-start > max_length/2-1:
+                head = ' ... '
+                start += 5
+                break
+        tail = ''
+        end = self.pointer
+        while end < len(self.buffer) and self.buffer[end] not in u'\0\r\n\x85\u2028\u2029':
+            end += 1
+            if end-self.pointer > max_length/2-1:
+                tail = ' ... '
+                end -= 5
+                break
+        snippet = self.buffer[start:end].encode('utf-8')
+        return ' '*indent + head + snippet + tail + '\n'  \
+                + ' '*(indent+self.pointer-start+len(head)) + '^'
+
+    def __str__(self):
+        snippet = self.get_snippet()
+        where = "  in \"%s\", line %d, column %d"   \
+                % (self.name, self.line+1, self.column+1)
+        if snippet is not None:
+            where += ":\n"+snippet
+        return where
 
 class YAMLError(Exception):
     pass
 
+class MarkedYAMLError(YAMLError):
+
+    def __init__(self, context=None, context_marker=None,
+            problem=None, problem_marker=None):
+        self.context = context
+        self.context_marker = context_marker
+        self.problem = problem
+        self.problem_marker = problem_marker
+
+    def __str__(self):
+        lines = []
+        #for (place, marker) in [(self.context, self.context_marker),
+        #                        (self.problem, self.problem_marker)]:
+        #    if place is not None:
+        #        lines.append(place)
+        #        if marker is not None:
+        #            lines.append(str(marker))
+        if self.context is not None:
+            lines.append(self.context)
+            if self.context_marker is not None  \
+                and (self.problem is None or self.problem_marker is None
+                        or self.context_marker.name != self.problem_marker.name
+                        or self.context_marker.line != self.problem_marker.line
+                        or self.context_marker.column != self.problem_marker.column):
+                lines.append(str(self.context_marker))
+        if self.problem is not None:
+            lines.append(self.problem)
+            if self.problem_marker is not None:
+                lines.append(str(self.problem_marker))
+        return '\n'.join(lines)
+
+
+