diff -r e46fa477007b -r 66c9591b733d linetypes.py
--- a/linetypes.py	Fri May 24 15:32:10 2019 +0300
+++ b/linetypes.py	Fri May 24 17:37:10 2019 +0200
@@ -16,24 +16,27 @@
     def typename(self):
         return 'empty line'
 
+class MetaCommand:
+    def __init__(self, text, style = 'old'):
+        self.text = text
+    def __repr__(self):
+        return str.format('linetypes.MetaCommand({text!r})',
+            text = self.text,
+        )
+    def textual_representation(self):
+        return ('0 ' + self.text).strip()
+    def typename(self):
+        return 'metacommand'
+
 class Comment:
     def __init__(self, text, style = 'old'):
-        if style == 'old' and text.startswith('//'):
-            self.text = text[2:].strip()
-            self.style = 'new'
-        else:
-            self.text = text
-            self.style = style
+        self.text = text
     def __repr__(self):
-        return str.format('linetypes.Comment({text!r}, {style!r})',
+        return str.format('linetypes.Comment({text!r})',
             text = self.text,
-            style = self.style,
         )
     def textual_representation(self):
-        if self.style == 'old':
-            return '0 ' + self.text
-        else:
-            return '0 // ' + self.text
+        return '0 //' + self.text
     def typename(self):
         return 'comment'
 
@@ -113,3 +116,16 @@
         return result
     def typename(self):
         return 'contour line segment'
+
+class Error:
+    def __init__(self, line, reason):
+        self.line = line
+        self.reason = reason
+    def __repr__(self):
+        return str.format(
+            'linetypes.Error(line = {line!r}, reason = {reason!r})',
+            line = self.line,
+            reason = self.reason,
+        )
+    def textual_representation(self):
+        return self.line