HTML-CSS and SVG output: minimal height for mover base [was [TeX input] \quad has no height]

[pkra]

It seems real (La)TeX considers \quad to have a height but the TeX input jax only produces an mspace with width.

An example (distilled from a journal article):

\widehat{\quad}: O \to Y

produces

<math display="block">
  <mrow class="MJX-TeXAtom-ORD">
    <mover>
      <mspace width="1em" />
      <mo>&#x005E;<!-- ^ --></mo>
    </mover>
  </mrow>
  <mo>:</mo>
  <mi>O</mi>
  <mo stretchy="false">&#x2192;<!-- → --></mo>
  <mi>Y</mi>
</math>

but the following is closer to rendering in real LaTeX:

<math display="block">
  <mrow class="MJX-TeXAtom-ORD">
    <mover>
      <mspace width="1em" height="0.5em" />
      <mo>&#x005E;<!-- ^ --></mo>
    </mover>
  </mrow>
  <mo>:</mo>
  <mi>O</mi>
  <mo stretchy="false">&#x2192;<!-- → --></mo>
  <mi>Y</mi>
</math>

[dpvc]

No, \quad has no height in TeX; it is just horizontal space, like in MathJax. I suspect that the accent code has a minimum height for the base that isn't in MathJax. If you look at \widehat{} in both LaTeX and MathJax, you'll see the difference.

[dpvc]

PS, CommonHTML does have the minimum height, but HTML-CSS and SVG don't.

[pkra]

Thanks. I renamed the issue.

[pkra]

@dpvc do you have any suggestion for a workaround? (This issue came up in production.)

[dpvc]

@pkra, you could use

\widehat{\vphantom{x}\quad}

if you want a source-level solution. It would also be possible to use a pre-filter to modify the input to replace \widehat{\quad} with \widehat{\vphantom{x}}. Or you could use an input post-filter to scan the produced MathML for an <mover> with an <mspace> as a base, and add the hight to it. Finally, it would be possible to override the TeX input jax's Accent method so that it checks if the base is an <mspace> and adds the height attribute. Something like

MathJax.Hub.Config({
  TeX: {Parse: {prototype: {
    Accent: function (name,accent,stretchy) {
      var c = this.ParseArg(name);
      if (c.isa(MML.mspace) && c.height == null) c.height = "1ex";
      var def = {accent: true}; if (this.stack.env.font) {def.mathvariant = this.stack.env.font}
      var mml = this.mmlToken(MML.mo(MML.entity("#x"+accent)).With(def));
      mml.stretchy = (stretchy ? true : false);
      var mo = (c.isEmbellished() ? c.CoreMO() : c);
      if (mo.isa(MML.mo)) mo.movablelimits = false;
      this.Push(MML.TeXAtom(MML.munderover(c,null,mml).With({accent: true})));
    }
  }}}
});

should do it (but I haven't tested it).

[pkra]

Thanks!

[dpvc]

The issue1706 branch of my fork of MathJax includes a fix.

[dpvc]

==> Merged

[dpvc]

==> In testsuite

MathMLToDisplay/Presentation/ScriptsAndLimits/issue1706.html