code: def rfc2425encode(name,value,parameters=None,charset="utf-8"):
      
      if not parameters:
          parameters={}
      if type(value) is unicode:
          value=value.replace(u"\r\n",u"\\n")
          value=value.replace(u"\n",u"\\n")
          value=value.replace(u"\r",u"\\n")
          value=value.encode(charset,"replace")
      elif type(value) is not str:
          raise TypeError("Bad type for rfc2425 value")
      elif not valid_string_re.match(value):
          parameters["encoding"]="b"
          value=binascii.b2a_base64(value)
  
      ret=str(name).lower()
      for k,v in parameters.items():
          ret+=";%s=%s" % (str(k),str(v))
      ret+=":"
      while(len(value)>70):
          ret+=value[:70]+"\r\n "
          value=value[70:]
      ret+=value+"\r\n"
      return ret
docs: Encodes a vCard field into an RFC2425 line.
  
      :Parameters:
          - `name`: field type name
          - `value`: field value
          - `parameters`: optional parameters
          - `charset`: encoding of the output and of the `value` (if not
            `unicode`)
      :Types:
          - `name`: `str`
          - `value`: `unicode` or `str`
          - `parameters`: `dict` of `str` -> `str`
          - `charset`: `str`
  
      :return: the encoded RFC2425 line (possibly folded)
      :returntype: `str`