Under "How does this work?", the post refers to the text in RFC 5895: > map characters to the "Simple_Lowercase_Mapping" property (the fourteenth column) in <h

Under "How does this work?", the post refers to the text in RFC 5895: > map characters to the "Simple_Lowercase_Mapping" property (the fourteenth column) in <http://www.unicode.org/Public/UNIDATA/UnicodeData.txt> http://www.unicode.org/Public/UNIDATA/UnicodeData.txt>, if any. as if that were responsible for turning ℡ into TEL. But the fourteenth column in > 2121;TELEPHONE SIGN;So;0;ON;<compat> 0054 0045 004C;;;;N;T E L SYMBOL;;;; is empty! What we're actually seeing is a Compatibility Decomposition, used when Unicode normalisation form NFKC is applied to the text. Whether it's appropriate for browsers to be applying NFKC may be questionable. RFC 5895 calls for the use of NFC (which would not apply mappings like this), but it also says that > These form a minimal set of mappings that an application should strongly consider doing. Of course, there are many others that might be done. which leaves things rather open.