Web Design in a Nutshell, 3rd Edition

Directionality

HTML 4.01 and XHTML take into account that many languages read from right to left and provide attributes for handling the directionality of text. Directionality is part of a character’s encoding within Unicode.

The dir attribute is used for specifying the direction in which the text should be interpreted. It can be used in conjunction with the lang attribute and may be added within the tags of most elements. The accepted value for direction is either ltr for “left to right” or rtl for “right to left.” For example, the following code indicates that the paragraph is intended to be displayed in Arabic, reading from right to left:

    <p lang="ar" xml:lang="ar"dir="rtl">...</p>

The bdo element, introduced in HTML 4.01, also deals specifically with documents that contain combinations of left- and right-reading text (bidirectional text, or bidi, for short). The bdo element is used for “bidirectional override,” in other words, it specifies a span of text that should override the intrinsic direction (as inherited from Unicode) of the text it contains. The bdo element uses the dir attribute as follows:

<bdo dir="ltr"> English phrase in an otherwise Hebrew text</bdo>...