The only correct approach for UTF-8 strings in Perl

The only correct approach for UTF-8 strings in Perl.

A string is treated as byte sequences without any flags.

Separate functions that handle UTF-8 from functions that handle byte sequences. The following is an example of the substr function.

substr_bytes
substr_utf8

The use utf8_func pragma replaces substr with substr_utf8.

The use bytes_func pragma replaces substr with substr_bytes.

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