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The recode reference manual

8.3 ASCII 7-bits, BS to overstrike

This charset is available in recode under the name ASCII-BS, with BS as an acceptable alias.

The file is straight ASCII, seven bits only. According to the definition of ASCII, diacritics are applied by a sequence of three characters: the letter, one BS, the diacritic mark. We deviate slightly from this by exchanging the diacritic mark and the letter so, on a screen device, the diacritic will disappear and let the letter alone. At recognition time, both methods are acceptable.

The French quotes are coded by the sequences: < BS " or " BS < for the opening quote and > BS " or " BS > for the closing quote. This artificial convention was inherited in straight ASCII-BS from habits around Bang-Bang entry, and is not well known. But we decided to stick to it so that ASCII-BS charset will not lose French quotes.

The ASCII-BS charset is independent of ASCII, and different. The following examples demonstrate this, knowing at advance that `!2' is the Bang-Bang way of representing an e with an acute accent. Compare:

% echo \!2 | recode -v bang..l1/d Request: Bang-Bang..ISO-8859-1/Decimal-1 233, 10

with:

% echo \!2 | recode -v bang..bs/d Request: Bang-Bang..ISO-8859-1..ASCII-BS/Decimal-1 39, 8, 101, 10

In the first case, the e with an acute accent is merely transmitted by the Latin-1..ASCII mapping, not having a special recoding rule for it. In the Latin-1..ASCII-BS case, the acute accent is applied over the e with a backspace: diacriticised characters have special rules. For the ASCII-BS charset, reversibility is still possible, but there might be difficult cases.