Interpretation of spaceAfterScript for mmultiscripts's prescripts #217

fred-wang · 2024-01-26T11:01:16Z

I stumbled on some interop issue while exporting tests from Gecko.

From https://learn.microsoft.com/en-us/typography/opentype/spec/math:

spaceAfterScript Extra white space to be added after each subscript and superscript. Suggested: 0.5 pt for a 12 pt font. (Note that, in some math layout implementations, a constant value, such as 0.5 pt, may be used for all text sizes. Some implementations may use a constant ratio of text size, such as 1/24 of em.)

MathML Core and Chromium places the space before each prescript at https://w3c.github.io/mathml-core/#base-with-prescripts-and-postscripts:

For each subscript/superscript pair of mmultiscripts prescripts:
Increment inline-offset by SpaceAfterScript.
...

But Firefox seems to do it the other way around, i.e. place the space after each prescript.

So the former option makes the rendering more symmetric with respect to the base, but the latter makes it more consistent with the parameter name.

Since we have space between scripts anyway, the significant difference is that the former adds a space between the leftmost scripts (assuming LTR) and the content before ; and the latter adds a space between the base and its closest prescripts.

fred-wang · 2024-01-26T11:14:01Z

Tentative test: unfortunately, scripts-spaceafterscript3000.woff cannot be access due to CORS policy. It seems chromium badly computes the inline size of mmultitscripts BTW.

<!DOCTYPE html>
<style>
  math {
    font: 50px spaceafterscript3000;
  }
  mspace {
      background: black
  }
  mmultiscripts {
      background: gray;
  }
  @font-face {
    font-family: spaceafterscript3000;
    src: url("http://wpt.live/fonts/math/scripts-spaceafterscript3000.woff");
  }
</style>
<math>
  <mmultiscripts>
    <mspace width="1em" height="1em" depth="1em"/>
    <mspace width="1em" height="1em" depth="1em"/>
    <mspace width="2em" height="1em" depth="1em"/>
    <mspace width="3em" height="1em" depth="1em"/>
    <mspace width="4em" height="1em" depth="1em"/>
    <mprescripts/>
    <mspace width="1em" height="1em" depth="1em"/>
    <mspace width="2em" height="1em" depth="1em"/>
    <mspace width="3em" height="1em" depth="1em"/>
    <mspace width="4em" height="1em" depth="1em"/>
  </mmultiscripts>
</math>

NSoiffer · 2024-01-29T17:17:54Z

I would tend to lean towards symmetry. Do you have any idea what TeX does for the equivalent {}_{sub}_{sup}{base}_{sub}_{sup}?

I'm not completely sure that is right comparison though. The mhchem package for ${}^{238}\text{U}$ does a lot of tweaking for spacing, so maybe that is a better indicator of what is right. It's a mess though:

<math>
        <mrow>
          <msubsup>
            <mrow>
              <mrow>
                <mpadded width='0'>
                  <mphantom>
                    <mi>A</mi>
                  </mphantom>
                </mpadded>
              </mrow>
            </mrow>
            <mrow>
              <mrow>
                <mpadded height='0' depth='0'>
                  <mphantom></mphantom>
                </mpadded>
              </mrow>
            </mrow>
            <mrow>
              <mrow>
                <mpadded height='0' depth='0'>
                  <mphantom>
                    <mn>238</mn>
                  </mphantom>
                </mpadded>
              </mrow>
            </mrow>
          </msubsup>
          <mspace width='-0.083em' linebreak='nobreak'></mspace>
          <msubsup>
            <mrow>
              <mrow>
                <mpadded width='0'>
                  <mphantom>
                    <mi>A</mi>
                  </mphantom>
                </mpadded>
              </mrow>
            </mrow>
            <mrow>
              <mrow>
                <mpadded width='0'>
                  <mphantom>
                    <mn>2</mn>
                  </mphantom>
                </mpadded>
              </mrow>
              <mrow>
                <mpadded width='0' lspace='-1width'>
                  <mrow>
                    <mpadded height='0'></mpadded>
                  </mrow>
                </mpadded>
              </mrow>
            </mrow>
            <mrow>
              <mrow>
                <mpadded height='0'>
                  <mrow>
                    <mpadded width='0'>
                      <mphantom>
                        <mn>2</mn>
                      </mphantom>
                    </mpadded>
                  </mrow>
                </mpadded>
              </mrow>
              <mrow>
                <mpadded width='0' lspace='-1width'>
                  <mn>238</mn>
                </mpadded>
              </mrow>
            </mrow>
          </msubsup>
          <mrow>
            <mi mathvariant='normal'>U</mi>
          </mrow>
        </mrow>
      </math>

dginev · 2024-01-29T17:47:20Z

So the former option makes the rendering more symmetric with respect to the base, but the latter makes it more consistent with the parameter name.

I guess one can view the symmetric approach to have a reading of "After" that means "AwayFromBase", or "Outer". "After" is a bit of an unfortunate preposition, since it depends on an implied traversal order...

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1876684 gecko-commit: eb00222e557742d5a6c66534f38345ddf71deaa5 gecko-reviewers: emilio

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1876684 gecko-commit: eb00222e557742d5a6c66534f38345ddf71deaa5 gecko-reviewers: emilio

fred-wang · 2024-02-02T12:40:21Z

I stumbled on some interop issue while exporting tests from Gecko.

For the record this is the == reftest (note: this is using RTL mmultiscript):
http://wpt.live/mathml/presentation-markup/direction/direction-overall-003.html
http://wpt.live/mathml/presentation-markup/direction/direction-overall-003-ref.html

The results are not available yet, but they should appear at:
https://wpt.fyi/results/mathml/presentation-markup/direction/direction-overall-003.html?label=experimental&label=master&aligned

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702 UltraBlame original commit: eb00222e557742d5a6c66534f38345ddf71deaa5

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1876684 gecko-commit: eb00222e557742d5a6c66534f38345ddf71deaa5 gecko-reviewers: emilio

khaledhosny · 2024-02-22T14:54:05Z

I tested with MS Word, and spaceAfterScript is added before prescripts (the test font uses a large value to make it obvious):

khaledhosny · 2024-02-22T15:40:46Z

I submitted MicrosoftDocs/typography-issues#1135 for clarifying this in OpenType spec.

fred-wang · 2024-02-22T15:48:11Z

I tested with MS Word, and spaceAfterScript is added before prescripts (the test font uses a large value to make it obvious):

Thanks Khaled, so this would consistent with MathML Core / Chromium. What is your test? It seems there is only one prescript and presubscript, right? Because I only see one gap.

khaledhosny · 2024-02-22T15:51:43Z

It seems there is only one prescript and presubscript, right?

Yes. Perhaps this screenshot makes it more obvious:

fred-wang · 2024-02-22T15:53:53Z

OK, I was asking because MathML supports multiple sub/sup pairs of prescripts, so we have a more generic use of spaceAfterScript: https://w3c.github.io/mathml-core/#figure-box-mmultiscripts

khaledhosny · 2024-02-22T16:01:08Z

I don’t think Microsoft Word support multiple pairs on either side.

- dir-3.html/dir-5.html: These are approximative verifications of overall RTL directionality using "covering rectangles". Export them with a a specific font in order to make them a bit more robust. For dir-5.html we use scripts-spaceafterscript3000.woff and adjust the rects accordingly but the test might change later depending on the outcome of w3c/mathml-core#217. - dir-4-ref.html: Removed (the test was removed in bug 1783995). Differential Revision: https://phabricator.services.mozilla.com/D199702 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1876684 gecko-commit: eb00222e557742d5a6c66534f38345ddf71deaa5 gecko-reviewers: emilio

fred-wang · 2024-09-18T10:05:34Z

@khaledhosny So IIUC the conclusion is that the space should be added before pre-scripts (and after post-scripts) so the "symmetric" approach by Chromium, not the "always-after-scripts" approach by Firefox.

khaledhosny · 2024-09-18T18:16:13Z

Yes. The spec text was also updated to make this more explicit:

Extra white space to be added after each subscript and superscript that occurs after a baseline element, and before each subscript and superscript that occurs before a baseline element.

fred-wang added css/html5 opentype/tex labels Jan 26, 2024

moz-wptsync-bot mentioned this issue Feb 1, 2024

[Gecko Bug 1876684] Export MathML dir-* tests to WPT. web-platform-tests/wpt#44351

Merged

khaledhosny mentioned this issue Feb 22, 2024

[MATH] Clarify spaceAfterScript in relation to pre-scripts MicrosoftDocs/typography-issues#1135

Closed

bkardell mentioned this issue Feb 25, 2024

MathML-Core (Rescheduled) Feb 27, 2024 Agenda #221

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Interpretation of spaceAfterScript for mmultiscripts's prescripts #217

Interpretation of spaceAfterScript for mmultiscripts's prescripts #217

fred-wang commented Jan 26, 2024

fred-wang commented Jan 26, 2024

NSoiffer commented Jan 29, 2024

dginev commented Jan 29, 2024

fred-wang commented Feb 2, 2024

khaledhosny commented Feb 22, 2024 •

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khaledhosny commented Sep 18, 2024

Interpretation of spaceAfterScript for mmultiscripts's prescripts #217

Interpretation of spaceAfterScript for mmultiscripts's prescripts #217

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fred-wang commented Jan 26, 2024

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