HTML..XHTML.The.Definitive.Guide..5th.Ed.1002002 [Electronic resources] نسخه متنی

3.10 The <bdo> Tag

As we
mentioned earlier, the authors of the HTML 4 standard made a
concerted effort to include standard ways that web agents (browsers)
are supposed to treat and display the many different human languages
and dialects. Accordingly, the HTML 4 standard and its progeny,
XHTML, contain the universal dir and
lang attributes that let you explicitly advise the
browser that the whole document or specific tagged segments within it
are in a particular language. These language-related attributes,
then, may affect some display characteristics; for example, the
dir attribute tells the browser to write the
words across the display from either left to right
(dir=ltr), as for most Western languages, or right
to left (dir=rtl), as for many Asian languages.
[Section 3.6.1.1] [Section 3.6.1.2]

The various Unicode and ISO standards for language encoding and
display may conflict with your best intentions. In particular, the
contents of some other documents, such as a MIME-encoded file, may
already be properly formatted, and your document may misadvise the
browser to undo that encoding. Hence, the HTML 4 and XHTML standards
have the <bdo> tag. With it, you override
any current and inherited dir specifications. And
with the tag's required dir
attribute, you definitively specify the direction in which the
tag's contents should be displayed.

For example, Figure 3-4 shows how Internet Explorer
6 handles the following HTML fragment containing a
<bdo> redirection:

<bdo dir=rtl>This would be readable if in Chinese, perhaps.</bdo>
Back to the Western way of reading and writing.

Figure 3-4. Tricks with <bdo> redirected text flow

Admittedly, the effects of the <bdo> tag are
a bit esoteric, and the opportunities to use it currently are rare.