It was designed for backward compatibility with ASCII. Code points with lower numerical values, which computerphile bitcoin chart to occur more frequently, are encoded using fewer bytes. The first 128 characters of Unicode, which correspond one-to-one with ASCII, are encoded using a single octet with the same binary value as ASCII, so that valid ASCII text is valid UTF-8-encoded Unicode as well.
Note that the ASCII only figure includes web pages with any declared header if they are restricted to ASCII characters. UTF-8 has been the dominant character encoding for the World Wide Web since 2009, as it’s most popular in every country, and as of June 2018 accounts for 91. Since the restriction of the Unicode code-space to 21-bit values in 2003, UTF-8 is defined to encode code points in one to four bytes, depending on the number of significant bits in the numerical value of the code point. The following table shows the structure of the encoding. The x characters are replaced by the bits of the code point.
Backward compatibility: Backwards compatibility with ASCII and the enormous amount of software designed to process ASCII-encoded text was the main driving force behind the design of UTF-8. In UTF-8, single bytes with values in the range of 0 to 127 map directly to Unicode code points in the ASCII range. Single bytes in this range represent characters, as they do in ASCII. Fallback and auto-detection: UTF-8 provided backwards compatibility for 7-bit ASCII, but much software and data uses 8-bit extended ASCII encodings designed prior to the adoption of Unicode to represent the character sets of European languages.
Part of the popularity of UTF-8 is due to the fact that it provides a form of backward compatibility for these as well. Prefix code: The first byte indicates the number of bytes in the sequence. Reading from a stream can instantaneously decode each individual fully received sequence, without first having to wait for either the first byte of a next sequence or an end-of-stream indication. The length of multi-byte sequences is easily determined by humans as it is simply the number of high-order 1s in the leading byte. This means a search will not accidentally find the sequence for one character starting in the middle of another character. Sorting order: The chosen values of the leading bytes and the fact that the continuation bytes have the high-order bits first means that a list of UTF-8 strings can be sorted in code point order by sorting the corresponding byte sequences. The two leading zeros are added because, as the scheme table shows, a three-byte encoding needs exactly sixteen bits from the code point.