The first sentence says: "This element specifies that the alignment and reading order for this run shall be right to left."
It is not clear how alignment can apply to a run, which may be just a part of a line. Alignment applies to a line or a group of lines (paragraph)

Clean up the text a bit to be more clear specifying what is the main use of the RTL tag and how RTL and LTR text are being treated.
Also, make clear definition what the term alignment means. Something like "This element specifies the linguistic rules which shall be applied when the contents of this run are displayed."

"rtl (Right To Left Text)"

, page 213 .
Section 2.3.2.28

ed

Proposed Disposition of DIS 29500 Comment IL-0004 (Modified: 2008-01-02) Agreed, the current description is confusing and misleading; the following updated description will replace the version currently in Part 4, §2.3.2.28, page 213, lines 6­15 and page 214, lines 1­7: This element specifies whether the contents of this run shall have right-to-left characteristics. Specifically, the following behaviors are applied when this element’s val attribute is true (or an equivalent): 1. Formatting ­ When the contents of this run are displayed, all characters shall be treated as complex script characters. This means that the values of the bCs element (§2.3.2.2) and the iCs element (§2.3.2.15) shall be use to determine bold and italic formatting, that the cs/cstheme attributes on the rFonts element (§2.3.2.24) shall be used to determine the font face, and the szCs element (§2.3.2.37) shall be used to determine the font size. 2. Character Directionality Override ­ When the contents of this run are displayed, this property acts as a right-to-left override for characters which are classified as follows (using the Unicode Character Database): Weak types except European Number, European Number Terminator, Common Number Separator, Arabic Number and (for Hebrew text) European Number Separator Neutral types [Rationale: This override allows applications to store and utilize higher-level information beyond that implicitly derived from the Unicode Bidirectional algorithm. For example, if the string "first second" appears in a right-to-left paragraph inside a document, the Unicode algorithm would always result in "first second" at display time (since the neutral character is surrounded by strongly classified characters). However, if the whitespace was entered using a right-to-left input method (e.g. a Hebrew keyboard), then that character could be classified as RTL using this property, allowing the display of "second first" in a right-to-left paragraph, since the user explicitly asked for the space in a right-to-left context. end rationale] This element provides information used to resolve the (Unicode) classifications of individual characters as either L, R, AN or EN. Once this is determined, the line should be displayed subject to the recommendation of the Unicode BiDi algorithm in reordering resolved levels. This property shall not be used with strongly left-to-right text. Any behavior under that condition is unspecified. If this element is not present, the default value is to leave the formatting applied at previous level in the style hierarchy. If this element is never applied in the style hierarchy, then right to left characteristics shall not be applied to the contents of this run. [Example: Consider the following WordprocessingML content: "first second, ". This content might appear as follows within its parent paragraph: <w:p> <w:r> <w:t xml:space="preserve">first second, </w:t> </w:r> <w:r> <w:rPr> <w:rtl/> </w:rPr> <w:t></w:t> </w:r> <w:r> <w:rPr> <w:rtl/> </w:rPr> <w:t xml:space="preserve"> </w:t> </w:r> <w:r> <w:rPr> <w:rtl/> </w:rPr> <w:t></w:t> </w:r> </w:p> The presence of the rtl element on the second, third, and fourth runs specifies that: The formatting on those runs is specified using the complex-script property variants. The whitespace character is treated as right-to-left. end example] Similar Comments: ECMA-0023 ,