701315 - Placement of accents via mover on mo elements is offset in textstyle

Status: RESOLVED INVALID

(Core :: MathML, defect)

Description

[Andrew Stacey]

Attachment: Screenshot-4.png

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20100101 Firefox/7.0.1
Build ID: 20110928221858

Steps to reproduce:

In MathML, using <mover> to place an accent on top of an <mo> element results in an offset accent when the maths is in "textstyle".  In "displaystyle" it renders correctly.

Sample code:

<math display='inline' xmlns='http://www.w3.org/1998/Math/MathML'><mover><mo>⊗</mo><mo>^</mo></mover></math>

<math display='inline' xmlns='http://www.w3.org/1998/Math/MathML'><mstyle displaystyle='true'><mover><mo>⊗</mo><mo>^</mo></mover></mstyle></math>

<math display='block' xmlns='http://www.w3.org/1998/Math/MathML'><mover><mo>⊗</mo><mo>^</mo></mover></math>

<math display='inline' xmlns='http://www.w3.org/1998/Math/MathML'><mstyle textstyle='true'><mover><mo>⊗</mo><mo>^</mo></mover></mstyle></math>

The middle two render correctly, the outer two do not.  See attached screenshot.


Actual results:

The accent is offset from the character.


Expected results:

The accent should have been placed directly over the character.

Comment 1

[distler]

Attachment: testcase

Testcase added.

This is a Gecko Core/MathML bug, not a Firefox bug. Doesn't seem that I have the privileges to reclassify it.

Comment 2

[Frédéric Wang (:fredw)]

Is this bug related to bug 567718?

> This is a Gecko Core/MathML bug, not a Firefox bug. Doesn't seem that I have
> the privileges to reclassify it.

You may want to ask Gerv to upgrade your Bugzilla privileges:
https://developer.mozilla.org/en/What_to_do_and_what_not_to_do_in_Bugzilla

Comment 3

[distler]

> Is this bug related to bug 567718?

Probably. I see two things going on.

1. The accent (U+005E) is displaced.
2. It is unstretched.

The base (U+2297), in this case, is not a combining character. Moreover, changing the base, from an mo to an mi, makes the accent appear correctly-placed (as does setting displaystyle=true).

The behaviour, that we're seeing here, is a little like what you expect fron msub/msup/msubsup applied to "large operators", like Sum. There, the placement of the subscript/superscript changes from display to inline mode.

Comment 4

[Frédéric Wang (:fredw)]

(In reply to distler from comment #3)
> > Is this bug related to bug 567718?
> 
> Probably. I see two things going on.
> 
> 1. The accent (U+005E) is displaced.
> 2. It is unstretched.
> 
> The base (U+2297), in this case, is not a combining character. Moreover,
> changing the base, from an mo to an mi, makes the accent appear
> correctly-placed (as does setting displaystyle=true).
> 
> The behaviour, that we're seeing here, is a little like what you expect fron
> msub/msup/msubsup applied to "large operators", like Sum. There, the
> placement of the subscript/superscript changes from display to inline mode.

OK, so that's probably not bug 567718, rather this happens just because U+2297 is in the operator dictionary with movablelimits=true. One should verified this carefully, but I think the behavior is correct (according to the MathML REC). One can get the correct rendering by forcing movablelimits=false via an explicit attribute.

Comment 5

[distler]

Ah.

I was expecting the movablelimits attribute to apply to msub/msup/msubsup, but not to munder/mover/munderover.

Was that expectation incorrect?

Comment 6

[Frédéric Wang (:fredw)]

(In reply to distler from comment #5)
> Ah.
> 
> I was expecting the movablelimits attribute to apply to msub/msup/msubsup,
> but not to munder/mover/munderover.
> 
> Was that expectation incorrect?

It's the contrary, the purpose of the movablelimits is to draw munderover like msubsup to save vertical space in inline formulas.

http://www.w3.org/TR/MathML/chapter3.html#presm.munderover

Comment 7

[Frédéric Wang (:fredw)]

Attachment: correct markup, with movablelimits="false"

Comment 8

[Frédéric Wang (:fredw)]

I close this bug, because this is the correct behavior per the MathML REC