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Re: The mapping of phi

From: David Carlisle <davidc@nag.co.uk>
Date: Wed, 2 Apr 2008 16:55:30 +0100
Message-Id: <200804021555.m32FtUMc021367@edinburgh.nag.co.uk>
To: elharo@metalab.unc.edu
Cc: public-html@w3.org, www-math@w3.org

> Unicode cannot change a glyph becuase it never assigned a glyph in the
> first place.

But it can (and did) change the charts at unicode.org swapping the
sample characters for the straight and curly phi symbols. So when font
designers are putting the unicode tables into their fonts they can (and
did, and do) assign the straight phi to one or the other of two slots
depending on the age of the unicode documentation they are looking at.

This changed _after_ HTML 4 came out.

So, what should html5 (and xhtml, and mathml,...) do

If it keeps phi with the html4 uniocde number then that gives a feeling
of stability, but if the user is using newer fonts, the visual
appearance will change, even looking at old pages.

If on the other hand html5 updates the mapping of phi, then for people
using newer fonts they'll get the intended character, unless they
actually intended to get the other character (because they looked at what
their browser gives now, rather than any updated uniocde charts)

Of course there are similar problems for pages that use nummeric
references or character data, but there is less indirection there so you
can't do anything about it.

Currently (as far as I know) the mapping is the only difference between
xhtml1 (and html5) mapping and defined here:


The phi problem is flagged in that spec

    XHTML uses U+03C6 (decimal 966) GREEK SMALL LETTER PHI, in these
    files phi is defined as U+03D5 (decimal 981) GREEK PHI SYMBOL 

MathML3 will use the mappings derined there by reference.

I think it's essential that HTML5 agrees with the definitio there so
that it's easy for HTML5 to agree with any XML formats that choose to
reference that set. So long as HTML5 and XHTML2 groups can agree
on the mapping of phi, it's easy to ensure that  the xml-entity-names
agrees with both of them (I'll just change it to match)
There's no right answer, but I think html xhtml, mathml, docbook, etc
all ought to use the same answer, especially as there keep being
proposals (for html or even future  xml  versions) just to build in these
definitions and not need them to be explictly declared, that's a lot
easier if everyone agrees what the definition should be...


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Received on Wednesday, 2 April 2008 15:56:20 UTC

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