Chapter 10. the Internet

85

RFC 2045 (

http://www.faqs.org/rfcs/rfc2045.html

) and and RFC 2046 (

http://www.

faqs.org/rfcs/rfc2046.html

) determine the way to write non ASCII characters in the main

text of mail. On the other hand, RFC 2047 (

http://www.faqs.org/rfcs/rfc2045.html

)

describes 'encoded words' which is the way to write non ASCII characters in the header. It is like

that:

=?

encoding

?

conversion algorithm

?

data

?=

, where encoding is selected from the list of

charset

of

Content Type

header, algorithm is

Q

or

q

for quoted printable or

B

or

b

for base64, and data

is encoded data whose length is less than 76 bytes. If the data is longer than 75 bytes, it must be

divided into multiple encoded words. For example,

Subject: =?ISO 2022 JP?B?GyRCNEE7eiROJTUlViU4JSclLyVIGyhC?=

reads 'a subject written in Kanji' in Japanese (ISO 2022 JP, encoded by base64). Of course human

cannot read it.

10.2 WWW

WWW is a system that HTML documents (mainly; and files in other formats) are transferred using

HTTP protocol.

HTTP protocol is defined by RFC 2068 (

http://www.faqs.org/rfcs/rfc2068.html

). HTTP

uses headers like mails and

Content Type

header is used to describe the type of the contents.

Though

charset

parameter can be described in the header, it is rarely used.

RFC 1866 (

http://www.faqs.org/rfcs/rfc1866.html

) describes that the default encoding

for HTML is ISO 8859 1. However, many web pages are written in, for example, Japanese and

Korean using (of course) encodings different from ISO 8859 1. Sometimes the HTML document

describes:

which declares that the page is written in ISO 2022 JP. However, there many pages without any

declaration of encoding.

Web browsers have to deal with such a circumstance. Of course web browsers have to be able to

deal with every encodings in the world which is listed in MIME. However, many web browsers

can only deal with ASCII or ISO 8859 1. Such web browsers are useless at all for non ASCII or

non ISO 8859 1 people.

URL should be written in ASCII character, though non ASCII characters can be expressed using

%

nn sequence where nn is hexadecimal value. This is because there are no way to specify encoding.

Wester European people would treat it as ISO 8859 1, while Japanese people would treat it as

EUC JP or SHIFT JIS.