UTF-8 refers to Unicode Transformation Format 8-bit, which is a variable-width encoding that can represent every character in the Unicode character set that was designed for backward compatibility with ASCII.
UTF-8 encodes each Unicode character as a variable number of 1 to 4 octets. The number of octets depends on the integer value assigned to the character. UTF-8 is the default encoding for XML and has been the dominant character encoding on the web since 2010.
W3C has offered several reasons for the popularity of UTF-8:
- An HTML page can only be in one encoding, and UTF-8 can support many languages and accommodate many pages and forms.
- Barriers to using Unicode are very low; by January 2012, Google reported that over 60% of the Web in their sample used UTF-8.
- ASCII is a subset of UTF-8; all ASCII characters in UTF-8 use the same bytes as an ASCII encoding, helping with Interoperability.
- The HTML5 specification says "Authoring tools should default to using UTF-8 for newly-created documents."