Why is UTS #46 necessary?
Browsers and other client software need to support existing pages, which were constructed under the IDNA2003 interpretation of international domain names. They also need to continue meet their user’s expectations, such as being able to type in IDNs with capital letters, or to use the ideographic period in Japanese or Chinese domain names. In particular, the 4 “deviation” characters have the opportunity to cause significant security and usability problems; they and symbols can be phased out over time, but need some transitional support. UTS #46 provides a compatibility bridge that allows implementations to handle both IDNA2003 and IDNA2008 domain names. For the specification and more background information, see UTS #46.
