Don't recommend the use of — in HTML. That code, along with all other numeric character references in the 128-159 range, is actually forbidden by the HTML specs. It's still commonly implemented in browsers as an em dash, but this is only done for compatibility. Early web browsers were lax in implementing the standards and didn't fully support Unicode. Instead of interpreting numeric character references according to Unicode (where 151 is a non-printing control character), they incorrectly interpreted them according to the default or selected local character encoding, which was behavior expected by people who primarily authored and viewed documents (HTML and otherwise) in those encodings. On English/Western European versions of Windows this encoding was the "Windows-1252" encoding, which has the em dash assigned to position/byte 151. Coupled with Unicode ignorance and the fact that support for the proper references (— or — or —) was spotty, this led to widespread use of — to signify an em dash. Nowadays, the proper reference should be used.