For left-to-right sentences, for example, in English,
the proper base text direction is Left To Right (LTR), even if a sentence
includes Arabic, Hebrew, Urdu, or Farsi words. For right-to-left sentences,
for example, in Arabic or Hebrew, the proper base text direction is
Right To Left (RTL), even if a sentence includes English words or
numbers.
Determining whether a sentence is, for example, English
or Arabic, is not always easy. Examine the example sentence in
Directional run. This sentence is an Arabic
and Hebrew sentence and therefore has a right-to-left base text direction.
The directional runs must be laid out on the line one after the other
from right to left. The following example shows each directional run
enclosed in square brackets.
[.] [united states][ EHT OT TNEW I ,] [23][ SAW I NEHW]
Consecutive English words form a left-to-right directional
run even when they are embedded in an Arabic, Hebrew, or Urdu sentence.
Consecutive Arabic or Hebrew words form a right-to-left directional
run, even when embedded in an English sentence. The ordering of successive
directional runs depends on the value of the base text direction.
The natural text direction of a language, right to left
for Arabic, Hebrew, or Urdu and left to right for English, is inherent
in the script used to write the text and is independent of the component
direction, which is handled by the GUI mirroring mode, and of the
user locale. Even if the GUI of a product is not mirrored, bidirectional
text entered by the user of an application, that is, bidirectional
text that the user directly or indirectly introduces and sees through
a product’s GUI, should be displayed according to its natural
base text direction. The user should have control over document and
paragraph base text direction independently of the component direction
(GUI mirroring mode).
The base text direction of bidirectional text affects
its display. Consider how the string hello world
!, listed in logical order, that is, the order in
which the text is pronounced, is displayed when its base text direction
is changed.
With left-to-right base text direction, the string is
displayed:
hello world !
With right-to-left base text direction, the same string
is displayed:
! hello world
In the example of right-to-left base text direction the
exclamation mark (!) appears on the left side of the string.
The string is not displayed
as “! world hello” when the base text direction
is right to left. Even though the base text direction is right to
left, consecutive English words always constitute a left-to-right
directional run, so that each word is displayed left to right and
the progression of words in the run is also left to right.