Section 8: Language information and text direction

--- tags: HTML4 SPEC --- # Section 8: Language information and text direction - [dicument link](https://www.w3.org/TR/html401/struct/dirlang.html) - purpose: internationalization of HTML (`lang` and `dir` attribute) ## 8.1 Specifying the language of content: the `lang` attribute This attribute specifies the base language of an **element's attribute** values and **text content**. - Assisting search engines - Assisting speech synthesizers - Helping a **user agent** select glyph variants for high quality typography - Helping a **user agent** choose a set of quotation marks - Helping a **user agent** make decisions about hyphenation, ligatures, and spacing - Assisting spell checkers and grammar checkers ### 8.1.1 Language codes The `lang` attribute's value is a language code. Language codes consist of a **primary code** and a possibly empty series of **subcodes**: ``` language-code = primary-code ( "-" subcode )* ``` Example: `en` : English `en-US` : U.S. version of English `en-cockney` : Cockney version of English - Two-letter primary codes : language abbreviations - Two-letter subcode : country code ### 8.1.2 Inheritance of language codes An element **inherits** language code information according to the following order of precedence (highest to lowest): 1. The `lang` attribute set for the **element itself** 2. The **closest parent** element that has the `lang` attribute set 3. The **HTTP "Content-Language" header** (which may be configured in a server) 4. **User agent** default values and user preferences ### 8.1.3 Interpretation of language codes - A language code should be interpreted by user agents as a **hierarchy of tokens** rather than a single token. - should always favor an **exact match** Example: `<HTML lang="en-US">` 1. `en-US` 2. `en` ## 8.2 Specifying the direction of text and tables: the `dir` attribute This attribute specifies the base **direction** of directionally neutral text in an element's content and attribute values. - LTR: Left-to-right text - RTL: Right-to-left text Example: to express a Hebrew quotation, it is more intuitive to write `<Q lang="he" dir="rtl">...a Hebrew quotation...</Q>` ``` 希伯來語文字是用來撰寫希伯來語及猶太語言的字體，並在時間上早於英語數千年。希伯來文為雙向字串的一個範例，希伯來文的字母是以由右至左的方向讀寫，數字則是由左至右。 ``` [Example](https://www.w3schools.com/tags/tryit.asp?filename=tryhtml5_global_dir) ### 8.2.0 [希伯來語簡介](http://languagemystery.blogspot.com/2015/01/blog-post_10.html) 希伯來語（Hebrew）是古代猶太民族的通行語言，是現時世上最古老的語言之一，在宗教上具有崇高的地位，古時《聖經》和猶太教的典籍都是用希伯來語所寫。今天，以希伯來語為官方語言的國家有以色列。 - 希伯來語屬於閃米特語族（Semitic languages），文字的書寫方向是從右到左 - 希伯來語的書寫文字只有輔音（又稱子音，consonants），而沒有元音（又稱母音，vowels）舉例說，假設你見到一句英語： You should love your parents with all your heart. 以希伯來語來書寫，首先要脫掉每個詞語的元音變成： Y shld lv yr prnts wth ll yr hrt. 再從右到左的方向書寫變成： .trh ry ll htw stnrp ry vl dlhs Y ### 8.2.1 Introduction to the bidirectional algorithm Consider the following example text: ``` english1 HEBREW2 english3 HEBREW4 english5 HEBREW6 ``` The order of characters stored in computer: ``` 0 => e 1 => n ... 49 => 6 ``` The way to display this sentence depends on which language is **predominant**. - English ``` english1 2WERBEH english3 4WERBEH english5 6WERBEH <------ <------ <------ H H H -------------------------------------------------> E ``` - Hebrew ``` 6WERBEH english5 4WERBEH english3 2WERBEH english1 -------> -------> -------> E E E <------------------------------------------------- H ``` ### 8.2.2 Inheritance of text direction information 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 **Inline elements**, on the other hand, do not inherit the dir attribute. ### 8.2.3 Setting the direction of embedded text Bidirectional algorithm automatically reverses embedded character sequences according to their inherent directionality, see [8.2.1](#821-Introduction-to-the-bidirectional-algorithm). owever, in general only **one level** of embedding can be accounted for. ``` english1 HEBREW2 english3 HEBREW4 english5 HEBREW6 ``` - English ``` english1 2WERBEH english3 4WERBEH english5 6WERBEH <------ <------ <------ H H H -------------------------------------------------> E ``` - Hebrew ``` 6WERBEH english5 4WERBEH english3 2WERBEH english1 -------> -------> -------> E E E <------------------------------------------------- H ``` - **English for all sentence, Hebrew for part of sentence**: must supply additional information, which we do by delimiting the second embedding explicitly ``` english1 4WERBEH english3 2WERBEH english5 6WERBEH -------> E <----------------------- H <-------------------------------------------------> E ``` ```html english1 <SPAN dir="RTL">HEBREW2 english3 HEBREW4</SPAN> english5 HEBREW6 ``` ### 8.2.4 Overriding the bidirectional algorithm: the BDO element ``` <!ELEMENT BDO - - (%inline;)* -- I18N BiDi over-ride --> <!ATTLIST BDO %coreattrs; -- id, class, style, title -- lang %LanguageCode; #IMPLIED -- language code -- dir (ltr|rtl) #REQUIRED -- directionality -- > ``` `dir` is mandatory attribute specifies the base direction of the element's text content. - LTR: Left-to-right text. - RTL: Right-to-left text. Some situations may arise when the bidirectional algorithm results in **incorrect presentation**. The BDO element allows authors to **turn off** the bidirectional algorithm for selected fragments of text Consider a document containing the same text as before: ``` english1 HEBREW2 english3 HEBREW4 english5 HEBREW6 ``` the above might be formatted, including line breaks, as: ``` english1 2WERBEH english3 4WERBEH english5 6WERBEH ``` This conflicts with the bidirectional algorithm, because that algorithm would **invert** 2WERBEH, 4WERBEH, and 6WERBEH **a second time**, displaying the Hebrew words left-to-right instead of right-to-left. Solution: ```htmlembedded <PRE> <BDO dir="LTR">english1 2WERBEH english3</BDO> <BDO dir="LTR">4WERBEH english5 6WERBEH</BDO> </PRE> ``` ### 8.2.5 Character references for directionality and joining control Since ambiguities sometimes arise as to the directionality of certain characters, specification includes characters to enable their proper resolution. Some directional entities: ``` <!ENTITY zwnj CDATA "‌"--=zero width non-joiner--> <!ENTITY zwj CDATA "‍"--=zero width joiner--> <!ENTITY lrm CDATA "‎"--=left-to-right mark--> <!ENTITY rlm CDATA "‏"--=right-to-left mark--> ``` ### 8.2.6 The effect of style sheets on bidirectionality When an **inline element** that does not have a `dir` attribute is transformed to the style of a **block-level element** by a style sheet, it inherits the `dir` attribute from its closest parent block element When a **block element** that does not have a `dir` attribute is transformed to the style of an **inline element** by a style sheet, explicitly adding a `dir` attribute (assigned the inherited value) to the transformed element.

Syntax	Example	Reference
# Header	Header	基本排版
- Unordered List	Unordered List
1. Ordered List	Ordered List
- [ ] Todo List	Todo List
> Blockquote	Blockquote
Bold font	Bold font
Italics font	Italics font
~~Strikethrough~~	~~Strikethrough~~
19^th^	19^th
H~2~O	H₂O
++Inserted text++	Inserted text
==Marked text==	Marked text
[link text](https:// "title")	Link
![image alt](https:// "title")	Image
`Code`	`Code`	在筆記中貼入程式碼
```javascript var i = 0; ```	`var i = 0;`
:smile:		Emoji list
{%youtube youtube_id %}	Externals
$L^aT_eX$	L^aT_eX
:::info This is a alert area. :::	This is a alert area.