Limitations of X11R6 in Supporting Internationalization

Limitations of X11R6 in Supporting Internationalization

Since X is locale-independent, there are some limitations on its ability to support internationalization. The X protocol and Xlib specification, together with ANSI C and POSIX restrictions, have led to certain choices being made in X11R6. These are described in the following paragraphs.

Vertical Text

There is no built-in support for vertical text. Applications may draw strings vertically only by laying out the text manually.

Character Sets

In previous releases of X, there was no general support for character sets other than Latin 1. X11R6, however, does allow other character sets.

X11R6 includes the definition of the X Portable Character Set, which is required to exist in all locales supported by Xlib. There is no encoding defined for this set; it is only a character set. The set--which is similar to printable ASCII plus the newline and tab--consists of these characters:

abcdefghijklmnoqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ
0123456789
!"#$%&'()*+,-./:;<=>?@[\]^_'{|}~
<space> <tab> <newline>

The Host Portable Character Encoding is the encoding of the X Portable Character Set on the Xlib host. This encoding is part of X, and is thus independent of locale--the coding remains the same for all locales supported by the host.

Strings used or returned by Xlib routines are either in the Host Portable Character Encoding or a locale-specific encoding. The Xlib reference pages specify which encodings are used where. Some string constructs (such as TextProperty) contain information regarding their own encoding.

Xlib Interface Change

Full use of X11R6's internationalization features means calling some new routines supplied in the X11R6 Xlib. While all old Xlib applications work with the new Xlib, developers should change their code in places. These are described below.