Some particularly useful tags registered with IANA allow you to specify Traditional vs. Simplified Chinese. In the past it was necessary to distinguish the two by using something like zh-CN (Mainland China) for Simplified Chinese and zh-TW (Taiwan) for Traditional Chinese. Apart from the fact that this is mislabelled, you could not guarantee that others would recognize these conventions, or even follow them. For example, some people used zh-HK to represent Traditional Chinese. Now IANA makes available the tags zh-Hans and zh-Hant for Simplified and Traditional Chinese, respectively. The following two paragraphs illustrate the use of these tags.

<p lang="zh-Hans" xml:lang="zh-Hans">当世界需要沟通时，请用Unicode！</p>

<p lang="zh-Hant" xml:lang="zh-Hant">當世界需要溝通時，請用統一碼（Unicode）</p>

It is expected that these tags will persist for the foreseeable future, so it would be good to use them as soon as possible in order to improve future interoperability sooner rather than later.