Graphemes can extend to over 10 code points? wow! Is there any limit?
No, not in general. ☃ I can’t recall where I read some standard suggested leaving enough room for buffering of 10 of them. I’d though it was RFC 3454, but it does not appear to be.

Consider this example. If you paste that into a Mac Terminal window, you will see stacking a bit like this. That string has up to 21 \pM code points following a \PM one. Placed one \X grapheme per numbered line, that’s this: 

     1  Z\x{335}\x{32C}\x{32E}\x{32B}\x{31E}\x{32A}\x{356}\x{354}\x{31
+6}\x{369}\x{350}\x{313}\x{34C}\x{313}\x{30D}\x{36C}
     2  A\x{31D}\x{33A}\x{317}\x{31C}\x{32F}\x{331}\x{363}\x{350}\x{34
+6}\x{301}
     3  L\x{337}\x{32D}\x{35A}\x{33C}\x{320}\x{318}\x{34E}\x{308}\x{30
+0}\x{302}\x{30B}\x{345}
     4  G\x{329}\x{35A}\x{332}\x{355}\x{302}\x{36F}\x{31A}\x{362}\x{36
+1}
     5  O\x{337}\x{31C}\x{33C}\x{332}\x{33B}\x{300}\x{311}\x{358}\x{36
+2}
     6   \x{32C}\x{324}\x{32D}\x{317}\x{332}\x{317}\x{33A}\x{36B}\x{34
+B}\x{35D}
     7  W\x{335}\x{348}\x{354}\x{34E}\x{31E}\x{320}\x{332}\x{32F}\x{34
+C}\x{30C}\x{33E}\x{301}
     8  I\x{354}\x{353}\x{36A}\x{365}\x{306}\x{369}\x{36C}\x{300}\x{36
+B}\x{351}\x{310}\x{358}\x{360}
     9  L\x{323}\x{324}\x{349}\x{313}\x{350}\x{350}\x{30E}\x{312}\x{30
+1}
    10  L\x{316}\x{31F}\x{364}\x{30C}\x{305}\x{36C}\x{302}\x{300}\x{31
+5}
    11   \x{31F}\x{325}\x{323}\x{33C}\x{325}\x{352}\x{367}\x{36E}\x{36
+C}\x{352}\x{30B}\x{365}\x{352}\x{35D}
    12  C\x{31C}\x{325}\x{331}\x{318}\x{317}\x{353}\x{34D}\x{354}\x{31
+3}\x{312}\x{36D}\x{350}\x{307}\x{35C}
    13  O\x{335}\x{319}\x{330}\x{316}\x{353}\x{350}\x{307}\x{311}\x{30
+B}\x{369}\x{304}\x{361}
    14  M\x{34A}\x{369}\x{346}\x{34A}\x{34F}\x{330}\x{32B}\x{32D}\x{33
+3}\x{33C}\x{320}\x{34E}\x{361}\x{35D}
    15  E\x{33F}\x{346}\x{34F}\x{31E}\x{35E}
    16   \x{327}\x{31B}\x{330}\x{35A}\x{31C}\x{318}\x{31E}\x{32B}\x{33
+9}\x{349}\x{308}\x{301}\x{33D}\x{352}\x{352}\x{302}\x{350}\x{36E}\x{3
+4B}\x{30D}\x{358}
    17   \x{327}\x{31E}\x{319}\x{317}\x{32A}\x{333}\x{30D}\x{310}\x{30
+0}\x{30C}\x{368}\x{35C}
    18  D\x{317}\x{33C}\x{33E}\x{33E}
    19  O\x{318}\x{320}\x{313}\x{36F}\x{300}\x{36C}
    20   \x{31B}\x{33C}\x{329}\x{32E}\x{354}\x{363}\x{30A}\x{352}\x{33
+F}\x{30F}\x{36D}\x{306}
    21  N\x{347}\x{325}\x{324}\x{32F}\x{32E}\x{323}\x{316}\x{316}\x{36
+3}\x{313}\x{36B}\x{368}
    22  O\x{334}\x{322}\x{32F}\x{33C}\x{355}\x{32E}\x{33A}\x{330}\x{31
+7}\x{302}\x{313}\x{364}\x{36F}\x{345}
    23  T\x{318}\x{308}\x{301}\x{30E}\x{350}\x{303}
    24   \x{338}\x{328}\x{349}\x{329}\x{31F}\x{307}\x{342}\x{357}\x{36
+2}
    25  A\x{349}\x{31C}\x{31D}\x{325}\x{31D}\x{34E}\x{349}\x{317}\x{30
+0}\x{314}\x{366}\x{30A}\x{313}\x{350}\x{35F}
    26  N\x{32B}\x{359}\x{359}\x{319}\x{347}\x{32F}\x{359}\x{355}\x{30
+F}\x{34C}\x{365}\x{364}\x{365}\x{366}\x{350}\x{352}\x{303}\x{315}
    27  G\x{323}\x{35A}\x{316}\x{35A}\x{331}\x{34E}\x{363}\x{313}\x{35
+B}\x{30E}\x{36D}\x{304}\x{301}
    28  E\x{339}\x{31D}\x{323}\x{35A}\x{339}\x{317}\x{33B}\x{349}\x{36
+A}
    29  R\x{34D}\x{317}\x{359}\x{339}\x{351}\x{313}\x{35F}
    30   \x{32B}\x{325}\x{324}\x{316}\x{333}\x{33C}\x{355}\x{32F}\x{36
+A}\x{36E}\x{30C}\x{36E}\x{366}\x{361}
    31  Z\x{369}\x{34A}\x{350}\x{30D}\x{301}\x{30B}\x{34F}\x{35A}\x{32
+C}\x{326}\x{355}\x{32B}\x{319}\x{329}
    32  A\x{337}\x{355}\x{317}\x{318}\x{32C}\x{34D}\x{35B}\x{30D}\x{36
+D}\x{363}\x{36B}\x{36D}\x{31A}\x{362}\x{345}
    33  L\x{322}\x{316}\x{320}\x{32B}\x{30D}\x{366}\x{342}\x{302}\x{36
+D}\x{304}\x{35B}
    34  G\x{316}\x{319}\x{359}\x{353}\x{33A}\x{368}\x{306}\x{36C}
    35  O\x{335}\x{339}\x{32B}\x{35A}\x{349}\x{348}\x{323}\x{356}\x{31
+4}\x{357}\x{36E}

[download]

Which is really quite remarkable, isn’t it? Each line is just one grapheme long. The longest, line number 16, contains 22 code points, which when encoded as UTF‑8, requires 43 bytes of storage. All told, that particular string has 8 words, 35 graphemes (user‐visible characters), 434 code points (programmer‐visible characters), and in UTF‑8 occupies 833 bytes (filesystem‐visible characters).

Which shows why we avoid the word “characters” when talking about Unicode. :)

In reply to Re^7: Best Way to Get Length of UTF-8 String in Bytes? by tchrist
in thread Best Way to Get Length of UTF-8 String in Bytes? by Jim

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