16. XHTML Bi-directional Text Attribute Module


This section is normative.

The Bi-directional Text module defines the Bi-directional attribute collection.

16.1. Bi-directional Text Collection

dir = "ltr|rtl|lro|rlo"
This attribute allows the author to specify the direction of the element's text content. This direction affects the display of characters as defined in Unicode Standard Annex #9: The Bidirectional Algorithm [UAX9], and defines directional properties of text as defined by CSS2 [CSS2]. The default value of this attribute is ltr. Possible values are:


The Hebrew word for "Hebrew" is 
<span xml:lang="he">&#x5e2;&#x5d1;&#x5e8;&#x5d9;&#x5ea;</span>,
but since Hebrew letters have intrinsic right-to-left directionality,
I had to type the word starting from the letter "&#x5e2;",
i.e. <span xml:lang="he" dir="lro">&#x5e2;&#x5d1;&#x5e8;&#x5d9;&#x5ea;</span>.
This might display as an image of the example.

16.1.1. Inheritance of text direction information

The Unicode bidirectional algorithm requires a base text direction for text blocks. To specify the base direction of a block-level element, set the element's @dir attribute. The default value of the @dir attribute is ltr (left-to-right text).

When the @dir attribute is set for a block-level element, it remains in effect for the duration of the element and any nested block-level elements. Setting the @dir attribute on a nested element overrides the inherited value.

To set the base text direction for an entire document, set the @dir attribute on the html element.


<html xmlns="http://www.w3.org/1999/xhtml" dir="rtl">
<title><em>...a right-to-left title...</em></title>
<em>...right-to-left text...</em>
<p dir="ltr"><em>...left-to-right text...</em></p>
<p><em>...right-to-left text again...</em></p>

Inline-level elements, on the other hand, do not inherit the @dir attribute. This means that an inline element without a @dir attribute does not open an additional level of embedding with respect to the bidirectional algorithm.

An element is considered to be block-level if its presentation, when expressed in [CSS2], is display: block and inline-level if its presentation, when expressed in [CSS2], is display: inline.

16.1.2. The effect of style sheets on bidirectionality

In general, using style sheets (such as [CSS2] to change an element's visual rendering from the equivalent of display: block to display: inline or vice-versa is straightforward. However, because the bidirectional algorithm relies on the inline/block-level distinction, special care must be taken during the transformation.

When an inline-level element that does not have a @dir attribute is transformed to a block-level element by a style sheet, it inherits the @dir attribute from its closest parent block-level element to define the base direction of the block.

When a block-level element that does not have a @dir attribute is transformed to an inline-level element by a style sheet, the resulting presentation should be equivalent, in terms of bidirectional formatting, to the formatting obtained by explicitly adding a @dir attribute (assigned the inherited value) to the transformed element.

Implementations: RELAX NG, XML Schema

16.2. Issues

[XHTML 2] 15 Bi-directional text collection and embedded attributes? PR #7783
State: Approved
Resolution: Modify and Accept
User: None

The dir attribute does not apply to embedded content. The src attribute is not equivalent to an xml "include" - it is a reference to a (potentially) external resource that is rendered in the way appropriate to that resources type. But that rendering is done in the context of a separate renderer; ala the object element. Similary, the styling from stylesheets that apply to the parent document does not apply to any embedded content. The fact that your example is "text" does not really matter - text is no more special than any other embedded content. It is handled by however the user agent processes text content, but in a different context than the parent element. We will add text to the src attribute description to clarify this.