The following are study notes on the lang attribute in HTML. Welcome to exchange and learn!
The value of the lang attribute should follow BCP 47 - Tags for Identifying Languages.
Single zh and zh-CN are obsolete usages.
The main problem is that zh is not the language code now, but macrolang. The language codes that can be used are cmn (Mandarin), yue (Cantonese), wuu (Wu language), etc. I usually recommend writing zh-cmn instead of just cmn, mainly to consider compatibility (at least matching zh). There are many software and frameworks that have not been updated accordingly. The problem with
zh-CN is that in most cases it is marked in Simplified Chinese, but the region is used inappropriately, which results in the inability to match zh-SG (Singapore), which is also in Simplified Chinese. More typical are zh-TW and zh-HK. So actually zh-Hans / zh-Hant should be used to represent simplified and traditional Chinese. Then the complete writing method is zh-cmn-Hans, which means Mandarin/Mandarin written in simplified Chinese. Generally speaking, there is no need to add a region code, unless you want to express regional specificity, usually because the vocabulary is different (such as Wikipedia's Mainland Simplified Chinese and Singapore-Malaysian Simplified Chinese).
Example of how to tag:
1. Simplified Chinese page: html lang=zh-cmn-Hans
2. Traditional Chinese page: html lang=zh-cmn- Hant
3. English page: html lang=en
4. Audio of "Come Back", sung in Mandarin: audio lang=zh-cmn
5. "Broad Sea and Sky" 》Audio, sung in Cantonese: audio lang=yue
6. Audio of "Come in Bai Xiangxiang", sung in Shanghainese: audio lang=wuu
Note that the above are all audio, So the Hans/Hant mark should not be added.
7. The audio of "Final Faith" is sung bilingually, so the audio does not need to be marked with lang (if it must be marked, it can be marked with lang=mul), but the lyrics of each paragraph can be marked with p lang=en and p lang=zh-cmn mark (zh-cmn-Hans or zh-cmn-Hant can be used according to simplified or traditional).
8. The audio of "Uneasy" has no lyrics, so there is no need to mark it with lang (if you must mark it, you can use audio lang=zxx).
There are generally few cases where area codes need to be added, unless it is to emphasize the differences in Chinese usage in different regions. For example:
菠萝和鳳梨其实是同一种水果。只是大陆和台湾称谓不同，且新马一带的称谓也是不同的，称之为黄梨。
Of course, due to historical reasons, sometimes we have to continue to use zh-CN. For example, the Chinese Wikipedia follows the traditional zh-CN/zh-HK/zh-SG/zh-TW (according to the standard, zh-cmn-Hans-CN, zh-cmn-Hant-HK, zh-cmn-Hans should be used -SG,zh-cmn-Hant-TW). At this time, reasonable software behavior is to convert zh-CN, etc. into zh-cmn-Hans (that is, into the actual standard writing corresponding to the most common misuse).
In fact, there is also a certain lag in various relevant standards. For example, the CSS :lang selector does not support selecting only Simplified/Traditional Chinese (regardless of Chinese dialects such as cmn, yue, or min). The ideal situation is that CSS3 upgrades the syntax of the :lang selector, that is, the advanced matching algorithm in BCP 47, and supports writing methods such as :lang(*-Hans).
Update: Selectors Level 4 has added support for the BCP 47 advanced matching algorithm, that is, it supports the :lang(*-Hans) writing method.