Horizontal Tabs

Permitted Context: %text
Content Model: Empty!

The TAB element can be used when you want fine control over the horizontal positioning. The TAB element is used with the <tab id=name> attribute to define named tab stops. Subsequently, you can use the TAB element with the <tab to=name> attribute to move to the previously defined tab stop. This approach avoids the need to know the font metrics in advance. The TAB element, together with style sheets, allows conversion software to preserve layout information when importing documents created with conventional word processing software.

For example:

<p><b>noct<tab id=t1>ambulant</b> - walking at night<br>
<tab to=t1>(from Latin: <i>nox noctis</i> night + <i>ambulare</i> walk)

which is rendered as:

noctambulant - walking at night
    (from Latin: nox noctis night + ambulare walk)

The tab stop name (t1 in the example) should be unique within the current document and composed from an initial letter followed by letters, digits or hyphens.

Sometimes, you want to make the remainder of the line flush right while leaving the earlier words unmoved. This is possible with the align attribute. For example:

Left part of line<tab align=right>and right part of line.

which is rendered as:

Left part of line                               and right part of line.

Permitted Attributes

An SGML identifier used to name a new tab stop at the current position. The scope of the tab stop is the rest of the document.
Specifies the number of en units before the tab stop. The en is a typographical unit equal to half the point size. It allows authors to control the leading indent before text, e.g. in poetry, one might use: <TAB INDENT=6> to indent six en units at the start of a line. The INDENT attribute is not meaningful when combined with the TO attribute.
Specifies a previously defined tab stop (see ID attribute).
Lines are usually rendered according to the alignment option for the enclosing paragraph element. The ALIGN attribute can be used to explicitly specify the horizontal alignment:

Following text starts immediately after the designated tab stop (the default).
Following text up to next tab or line break is centered on the designated tab stop. If the TO attribute is missing, it centers the text between the current left and right margins.
Following text up to the next tab or line break is rendered flush right to the designated tab stop. If the TO attribute is missing, it renders the text flush right against the current right margin.
The following text is searched for the first occurrence of the character representing the decimal point. The text up to the next tab or line break is then aligned such that the decimal point starts at the designated tab stop. If the TO attribute is missing, the tab element is treated as a single space character.
This specifies the character to be used for the decimal point with the ALIGN attribute, e.g. dp="." (the default) or dp=",". The default may be altered by the language context, as set by the LANG attribute on enclosing elements.

Note: if the specified alignment and tab stop would cause text to overlap preceding text, then the tab element may be treated as a single space character.

How should the above be rewritten to work with languages which are rendered from right to left? What about lines with mixed directions?