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Re: Formula alignment

From: David Carlisle <davidc@nag.co.uk>
Date: Fri, 18 Dec 2015 17:20:31 +0000
To: <www-math@w3.org>
Message-ID: <5674405F.5070905@nag.co.uk>
On 18/12/2015 16:56, Daniel Marques wrote:
> Dear MathML group,
>
> I’m just wandering how to align formulas given a symbol. For example,
>
> __y=x+1
>
> x+1=y
>
> (where the _ are spaces)
>
> Reading the MathML specification, I came up with
>
> <mtable>
>
>    <mtd>
>
>      <mi>y</mi>
>
>      <malignmark/>
>
>      <mo> = </mo>
>
>     <mi>x</mi>
>
>      <mo>+</mo>
>
>      <mn>1</mn>
>
>    </mtd>
>
>   <mtd>
>
>      <mi>x</mi>
>
>      <mo>+</mo>
>
>      <mn>1</mn>
>
>      <malignmark/>
>
>      <mo> = </mo>
>
>      <mi>y</mi>
>
>    </mtd>
>
> </mtable>
>
> Do you think that this is the best way to express that?

Apart from a missing mtr (was optional in mathml 1 but not since)
yes but.....


malignmark is one of the trickier areas of mathml and not supported
in all mathml renderers so if you are targetting a specific system and
it works then fine, otherwise I'd split it as two columns right aligned
for the left hand side and left aligned for the rest. Of course that
suffers from the problem that malignmark was trying to address of
breaking up the expression structure.


>
> Another question is whether the malignmark must appear always inside a
> table (mtable)
as specified yes.

  or can be used also combined with <mspace
> linebreak="newline"/>. For example, is the following a valid alternative?
>
>    <mrow>
>
>      <mi>y</mi>
>
>      <malignmark/>
>
>      <mo> = </mo>
>
>     <mi>x</mi>
>
>      <mo>+</mo>
>
>      <mn>1</mn>
>
>      <mspace linebreak="newline"/>
>
>      <mi>x</mi>
>
>      <mo>+</mo>
>
>      <mn>1</mn>
>
>      <malignmark/>
>
>      <mo> = </mo>
>
>      <mi>y</mi>
>
>    </mrow>
>
> Dani
>

I was going to show that that was invalid but it turns out that
it is invalid according to the prose but the constraint that malignmark
only appears in tables isn't checked by the schema. (In principle it
could do but it would greatly complicate the relax schema as you'd have
to carry the fact that you were inside a table through arbitrary pattern
rules.  I suppose the XSD schema could have had an xpath assertion
saying explicitly that all malignmark are within a table.


David

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Received on Friday, 18 December 2015 17:21:10 UTC

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