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Re: Questions about indentshift

From: David Carlisle <davidc@nag.co.uk>
Date: Sat, 05 Apr 2014 21:54:59 +0100
Message-ID: <53406DA3.5090501@nag.co.uk>
To: www-math@w3.org
On 05/04/2014 20:41, Davide P. Cervone wrote:
> Neil:
> Thanks for getting back to me on this, but I'm afraid I'm still
> confused.  I wasn't asking about how indentshift relates to indentalign,
> but on how indentshiftfirst relates to indentshift.  A simplified
> version of the test that I cited is
> <math indentshift="3em" display="block">
>     <mrow>
>        <mi>a</mi>
>        <mspace linebreak="newline" />
>        <mo>+</mo>
>        <mi>b</mi>
>    </mrow>
> </math>
> Here, indentshift is 3em, so I understand that the plus sign will be 3em
> to the right of where it would have been if identshift were 0.  My
> question is where should the "a" be placed?  It should be controlled by
> the value of indentshiftfirst, but the default of indentshiftfirst is
> "inherited (indentshift)".  If I understand this right, the value of
> indentshiftfirst should be the value of indentshift, since there is no
> setting for indentshiftfirst.  So the first line should ALSO be 3em to
> the right of indentalign.
> So what I expect to see if BOTH the "a" and the "+" indented the SAME
> amount (3em).  But in the image for that test, the second line is 3em
> farther to the right of the position of the first line.  (Unless you
> mean that MathPlayer is using the <mrow> around the whole equation to
> say that the line break is nested, so needs to be indented further.  But
> that would mean that the first line would have to be considered as
> starting outside the <mrow>, which seems a bit of a stretch).

I think it's definitely the case that the image is the intended layout, 
your reading would mean the default layout if you had indented layout 
would be the first two lines were aligned which would be odd. On the 
other hand the wording in the spec could be clearer, although as you may 
note if you look at the editor's draft we don't have a lot of time to 
fiddle with the wording in this round...

If you say indentshift=3em then what you are specifying is that line
l is indented by (l-1)*3em.

What (I think) the spec wants to say is that if you specify 
indentshiftfirst or indentshiftlast then it over-rides the above formula 
for the respective lines. So the default value is "do what you would 
have done if only indentshift is set" not "the numerical value of 
indentshift". On the other hand it takes a "careful reading" of the 
current wording to deduce the above interpretation.

But I'd defer to Neil on the linebreaking algorithm, so this is very 
much a personal view.

Received on Saturday, 5 April 2014 20:55:29 UTC

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