RTF - proprietary or open?

[Celejar <celejar@gmail.com>]

I'm using Abiword, which recommends using RTF for document exchange
with non-Abi users.  I'm trying to understand whether RTF is an open
standard.  Wikipedia [0] claims that it's proprietary.  This article
[1] points out that it has the same status as PDF.  I can't imagine
that Abi would recommend a non-open standard, and even prefer it to ODF
(OASIS / XML) [2].  What does it even mean for a file format to be
open? That the creator can't restrict its use? That the spec has been
published?

[0] http://en.wikipedia.org/wiki/Rich_Text_Format
[1] http://www.tkachenko.com/blog/archives/000657.html
[2] http://www.abisource.com/mailinglists/abiword-dev/2003/Apr/0167.html

Celejar
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