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    <blockquote> <p>I am asking for the count of all the possible valid combinations in Unicode with explanation.</p> </blockquote> <p><strong>1,111,998</strong>: 17 planes &times; 65,536 characters per plane - 2048 surrogates - 66 noncharacters</p> <p>Note that UTF-8 and UTF-32 could theoretically encode much more than 17 planes, but the range is restricted based on the <a href="https://stackoverflow.com/questions/130438/do-utf-8-utf-16-and-utf-32-unicode-encodings-differ-in-the-number-of-characters">limitations of the UTF-16 encoding</a>.</p> <p><strong>109,384</strong> code points are actually assigned in <a href="http://www.unicode.org/versions/Unicode6.0.0/ch01.pdf" rel="noreferrer">Unicode 6.0</a>.</p> <blockquote> <p>I also don't understand why continuation bytes have restrictions even though starting byte of that char clears how long it should be.</p> </blockquote> <p>The purpose of this restriction in UTF-8 is to make the encoding <a href="http://en.wikipedia.org/wiki/Self-synchronizing_code" rel="noreferrer">self-synchronizing</a>.</p> <p>For a counterexample, consider the Chinese GB18030 encoding. There, the letter <code>ß</code> is represented as the byte sequence <code>81 30 89 38</code>, which contains the encoding of the digits <code>0</code> and <code>8</code>. So if you have a string-searching function not designed for this encoding-specific quirk, then a search for the digit <code>8</code> will find a false positive within the letter <code>ß</code>.</p> <p>In UTF-8, this cannot happen, because the non-overlap between lead bytes and trail bytes guarantees that the encoding of a shorter character can never occur within the encoding of a longer character.</p>
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    1. COThe "self-synchronizing" article you linked doesn't explain what's self-synchronizing at all
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