From: John Cowan (cowan@mercury.ccil.org)
Date: Wed Oct 22 2003 - 06:59:43 CST
Philippe Verdy scripsit:
> I also have some old documents that use <VT>=U+000B instead of
> LF=U+000A to increase the interparagraph spacing. This is still
> mapped to the source '\v' character constant in C/C++ (and Java
> as well, except that Java _requires_ that '\v' be mapped only to
> VT.
The XML Core WG also looked at FF, but decided that like PS it might
be markup, and therefore shouldn't arbitrarily be mapped to LF.
We didn't look at VT as far as I remember.
Historically and originally, VT was meant to control line printers,
which had a paper tape loop inside that selected the number of lines
per page, and was advanced by one frame for each line printed. A hole
punched in a certain column represented line 1, and so FF was implemented
by advancing the tape and the paper until this hole was detected. Another
column could contain holes for vertical tabulation points, and VT advanced
the tape and paper until the next such hole was reached. Thus VT was
strictly analogous to TAB.
> Some applications still seem to use <VT> after <CR> to create soft line
> breaks, in text files where paragraphs are normally ended by <CR><LF>.
IIRC, Microsoft Word uses VT internally to indicate a hard line break,
and CR for a paragraph break.
> CR was intended to create an overstrike on the previously written (but
> still complete) line, for example to underline some characters on that
> line. This is what '\r' should imply in C, and in fact such '\r' should no
> more be used in C, as it relies to add visual attributes to the previous
> text. That why <CR> comes before <LF> that terminates the paragraph.
In addition, Teletype terminals that received <LF, CR> would not reliably
print the next character in the first horizontal position, because of
the time it took to execute a CR.
--
Not to perambulate John Cowan <jcowan@reutershealth.com>
the corridors http://www.reutershealth.com
during the hours of repose http://www.ccil.org/~cowan
in the boots of ascension. --Sign in Austrian ski-resort hotel
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