parameters: (self, line)
return_statement: return None
docstring: Determine whether a given line is a legal header.
  
          This method should return the header name, suitably canonicalized.
          You may override this method in order to use Message parsing on tagged
          data in RFC 2822-like formats with special header formats.
docstring_summary: Determine whether a given line is a legal header.
docstring_tokens: Determine whether a given line is a legal header .
function: def isheader(self, line):
          """Determine whether a given line is a legal header.
  
          This method should return the header name, suitably canonicalized.
          You may override this method in order to use Message parsing on tagged
          data in RFC 2822-like formats with special header formats.
          """
          i = line.find(':')
          if i > 0:
              return line[:i].lower()
          return None
function_tokens: def isheader ( self , line ) : i = line . find ( ':' ) if i > 0 : return line [ : i ] . lower ( ) return None