Description:
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The documentation for strlen() is inaccurate. From my tests it looks like strlen() returns the number of bytes in a string, not the number of characters.

Reproduce code:
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$str = '?';

echo 'strlen(€) when € is encoded in ANSI (only one byte long): ' . strlen(mb_convert_encoding($str, 'WINDOWS-1252'));
echo ' - strlen(€) when € is encoded in UTF-8 (two bytes long): ' . strlen(mb_convert_encoding($str, 'UTF-8'));

Expected result:
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strlen(?) when ? is encoded in ANSI (only one byte long): 1 - strlen(?) when ? is encoded in UTF-8 (only two bytes long): 1

Actual result:
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strlen(?) when ? is encoded in ANSI (only one byte long): 1 - strlen(?) when ? is encoded in UTF-8 (only two bytes long): 2