Thank you, Tux, for your reply.
If otoh 0xAE is just a placeholder for embedded newlines, that is easy to do (see below).
Yes, U+00AE (®, REGISTERED SIGN, 0xC2 0xAE in UTF-8) is used as a placeholder for literal newlines in quoted strings. The CSV records in Concordance DAT files are ordinary ones with standard EOL characters: <CR><LF> pairs.
Another point of care is that Text::CSV_XS does not deal with BOM's, so you'll need File::BOM or other means to deal with that.
This would be a nice feature to add to Text::CSV_XS: proper handling of Unicode byte order marks in UTF-8, UTF-16 and UTF-32 CSV files.
Note that the encoded U+00FE is 0xC3BE, which is two bytes, and two bytes cannot be used as a sep_char in Text::CSV_XS, which parses the data as bytes, so the stream has to be properly coded before parsing.
This settles it. It's not the answer I'd hoped for, but I'm glad to know now with certainty that Text::CSV_XS cannot parse a UTF-8 Concordance DAT file. I'll stop trying hopelessly to make it work. ;-)
How difficult would it be to enhance Text::CSV_XS to handle metacharacters in Unicode CSV files that are outside the Basic Latin block (i.e., not ASCII characters)? The Concordance DAT file is a de facto standard format for data interchange in the litigation support and e-discovery industry. As I've explained, the only thing special about it is the unusual and unfortunate characters it uses for metacharacters: U+0014, which is a control code; U+00FE, which is word constituent character; and U+00AE, which is a common character in ordinary text.