Text direction

Keep placeholders from reordering the text around them in mixed left-to-right and right-to-left text with MessageFormat 2's default bidi isolation strategy and the u:dir option.

When a Hebrew name sits inside an English sentence, or a number inside an Arabic one, the Unicode bidirectional algorithm can move the punctuation and words next to it to the wrong side. Bidi isolation wraps each placeholder in invisible control characters so it cannot affect its neighbors.

It is off by default. Turn it on for the formatter or the translator:

use dxn_i18n::{Args, BidiIsolation, Message, MessageFormatter};
use dxn_intl::parse_locale;

let message = Message::parse("{$name} has {$points :number} points")?;
let args = Args::new().with("name", "שלום").with("points", 5);

let plain = MessageFormatter::new(parse_locale("en")?);
assert_eq!(plain.format(&message, &args).text, "שלום has 5 points");

let isolated = plain.with_bidi_isolation(BidiIsolation::Default);
assert_eq!(isolated.format(&message, &args).text, "\u{2068}שלום\u{2069} has 5 points");

On a translator, call translator.set_bidi_isolation(BidiIsolation::Default). Message::format always uses BidiIsolation::None.

#What gets wrapped

With BidiIsolation::Default, a placeholder’s text is wrapped according to the direction of its value and of the message. The message’s direction is its locale’s script direction (ar and he are right to left).

So in an LTR message only text arguments are wrapped, and in an RTL message every placeholder is. A number formatted with u:locale of the other direction is wrapped in either kind of message. Fallbacks ({$name}) are never wrapped, and the isolates are part of the text of a Part::Value in parts.

use dxn_i18n::{Args, BidiIsolation, Message, MessageFormatter};
use dxn_intl::parse_locale;

let ar = MessageFormatter::new(parse_locale("ar")?).with_bidi_isolation(BidiIsolation::Default);
let message = Message::parse("{$n :number}")?;
let text = ar.format(&message, &Args::new().with("n", 5)).text;
assert_eq!(text, "\u{2067}5\u{2069}");

#Choosing the direction yourself

The u:dir option on a function sets the direction of its value: ltr, rtl, auto (the renderer decides, FSI) or inherit (the default). Use it where you know better, such as a phone number inside Arabic text, or a user-written name:

use dxn_i18n::{Args, BidiIsolation, Message, MessageFormatter};
use dxn_intl::parse_locale;

let ar = MessageFormatter::new(parse_locale("ar")?).with_bidi_isolation(BidiIsolation::Default);
let message = Message::parse("{$phone :string u:dir=ltr}")?;
let text = ar.format(&message, &Args::new().with("phone", "+385 1 234 5678")).text;
assert_eq!(text, "\u{2066}+385 1 234 5678\u{2069}");

An unknown value is a BadOption error and is treated as inherit. u:dir is an error on markup. Without bidi isolation turned on, the option has no effect on the text.

#Text direction in your UI

Isolation protects a sentence from its parts; it does not set the direction of the whole line. For that, ask dxn_intl for the locale’s direction and set your widget’s or HTML element’s dir from it:

use dxn_intl::{Direction, direction, parse_locale};

assert_eq!(direction(&parse_locale("ar")?), Direction::Rtl);
assert_eq!(direction(&parse_locale("hr")?).as_str(), "ltr");

dxn_intl is documented at dXn.Intl.

Next: Built-in functions.