I don't have much experience with bidi. I've been having a quick read
up on it, and there seem to be the following features. Correct me if
I’m wrong.
a) Unicode implicitly supports bidi. Write a span containing Hebrew
characters, and it will be laid out right to left. We don’t need to do
anything to support this.
b) <span dir="xxx"> and Unicode controls such as RIGHT-TO-LEFT
EMBEDDING, give hints about how to layout neutral characters such as
punctuation marks that are used between flows of ltr and rtl text. We
don’t need to do anything to support these Unicode controls. <span
dir> can be used in Text constructs if required, but such a mechanism
isn’t necessary for the rest of Atom.
HTML benefits from <span dir> because it is easier to type it in HTML
source than Unicode escapes, but nobody really types Atom source by
hand, and operating systems do support embedding of Unicode escapes
via text widgets (eg, on Windows, install supplemental language
support via Regional Settings control panel - I think?). Allowing dir
to be used anywhere in Atom does not provide the same feature as <span
dir>, because the sole purpose of it is to disambiguate mixed
directions *within* a flow of text, and allowing @dir anywhere in Atom
would not achieve that granularity.
c) <bdo dir="xxx"> and Unicode controls such as RIGHT-TO-LEFT OVERRIDE
allow the Unicode algorithm to be disabled and direction to be
hard-coded. Under what circumstances is this needed? Is it
appropriate for Atom?
d) <div dir="xxx"> sets the base direction of the text. One of the
effects of this is that <div dir="rtl"> makes paragraphs right
aligned, and table columns to be laid out right-to-left.
I'm not convinced that we need support for this in Atom. I'd like to
hear more opinions. In HTML it makes sense to specify that a block of
text is right-aligned, but in Atom there are no blocks of text; just
fields. Isn't this largely a presentation feature?
Adding an attribute that is supposed to inherit from feed elements to
entry elements is a breaking change to Atom that is likely to lead to
silent data-loss with existing implementations. Implementations would
need to know to inherit the attribute down to entries and store it
with the entries rather than with the feed, so that retrospective
changes don't change the direction of previously polled entries.
I think that inheritance is useful for a hierarchically structured
document like HTML, but confusing for Atom, which is essentially a
bunch of XML-ified structs with a fairly arbitrary hierarchy
representing multiple entities with seperate life-cycles. (People deal
with feeds containing a subset of all entries ever, not with feed
documents)
e) <html dir="xxx"> in IE at least, this affects not only the page,
but the layout of browser chrome such as scrollbars and Javascript
alerts. I don't think that this feature is appropriate for syndication
format. The user preferences of the user-agent (probably via the OS)
would probably be better suited to control the application layout.
So, the question is: do we need the ability to markup the "base
direction" of text in Atom, at a block level. If so, what are the
applications of the "base direction" in Atom's layout-agnostic fields
such as category label?
Also at what granularity do we need to do this? On every element, or
would it be sufficient to use extension elements to describe the base
direction at the entry/feed level (cf: <html dir>) ?
--
Dave
