Require that the encoding declaration is on a line of its own, to simplify

parsing.

pep-0263.txt

@@ -54,7 +54,9 @@ Defining the Encoding
     More precise, the first or second line must match the regular
     expression "coding[:=]\s*([\w-_.]+)". The first group of this
     expression is then interpreted as encoding name. If the encoding
-    is unknown to Python, an error is raised during compilation.
+    is unknown to Python, an error is raised during compilation. There
+    must not be any Python statement on the line that contains the
+    encoding declartation.
 
     To aid with platforms such as Windows, which add Unicode BOM marks
     to the beginning of Unicode files, the UTF-8 signature