Katex: Error with subscript or superscript

Created on 2 Dec 2018 · 11Comments · Source: KaTeX/KaTeX

Typing \log_{10}\left(x\right) into the preview at katex.org results in the error
Invalid markup: Incorrect number of children for <msub/> tag.
Same with
\log^{10}\left(x\right)

I am using Firefox 63.0.3 on Windows. The error does not occur on Chrome or Edge.

MathML bug

Source

JMSS-Unknown

All 11 comments

More related errors
\lim_{x\to\infty}
gives
Invalid markup: Incorrect number of children for <munder/> tag.

JMSS-Unknown on 2 Dec 2018

I tried reproducing these using the MacOS version of Firefox but wasn't able to. Could you paste the MathML markup that you're seeing when you get these errors?

kevinbarabash on 3 Dec 2018

For \log_{10}\left(x\right)

<span class="katex-mathml">
   <math>
      <semantics>
         <mrow>
            <msub>
               <mi>log</mi>
               <mo>⁡</mo>
               <mn>10</mn>
            </msub>
            <mrow>
               <mo fence="true">(</mo>
               <mi>x</mi>
               <mo fence="true">)</mo>
            </mrow>
         </mrow>
         <annotation encoding="application/x-tex">\log_{10}\left(x\right)</annotation>
      </semantics>
   </math>
</span>

JMSS-Unknown on 3 Dec 2018

It seems to be caused by the empty mo tag.
I extracted it to a new page to get:

<!DOCTYPE html>
<html>
   <head>
      <meta charset="utf-8">
   </head>
   <body>
      Equation:
      <span class="katex-mathml">
         <math>
            <semantics>
               <mrow>
                  <msub>
                     <mi>log</mi>
                     <mo>⁡</mo>
                     <mn>10</mn>
                  </msub>
                  <mrow>
                     <mo fence="true">(</mo>
                     <mi>x</mi>
                     <mo fence="true">)</mo>
                  </mrow>
               </mrow>
               <annotation encoding="application/x-tex">\log_{10}\left(x\right)</annotation>
            </semantics>
         </math>
      </span>
   </body>
</html>

With the mo tag I get invalid-markup, without it the log renders correctly.

JMSS-Unknown on 3 Dec 2018

I don't expect that the mo tag is actually empty. It should have an invisible character, U+2061 (⁡), inside it. This is intentional (though arguably it should be after the <msub>...).

However, I'm also unable to reproduce the error, using Firefox 63.0.3 on Windows. Could it be caused by a plugin? Can you try in a private window?

edemaine on 3 Dec 2018

The error still occurs in private browsing with all extensions disabled. I also just tried it on another computer and the error did not show up. Seems like it has something to do with my setup.

JMSS-Unknown on 3 Dec 2018

The error shows up if you select CSS under filter output in the console. Is this an issue?

JMSS-Unknown on 3 Dec 2018

👍1

With that instruction, I can reproduce the error. It seems to happen with \log_5 x but not \log x.

Ah, I see the issue now. <msub> is supposed to have only two children, but in this example, it has 3. This is caused by op's MathML builder returning a document fragment: https://github.com/KaTeX/KaTeX/blob/f71f469d4b3ca97654702a0807e736d176f4c4c5/src/functions/op.js#L251-L263

I think we need to modify supsub's MathML builder to wrap a fragment in an mrow, in this line: https://github.com/KaTeX/KaTeX/blob/f71f469d4b3ca97654702a0807e736d176f4c4c5/src/functions/supsub.js#L204

Alternatively, we need to bring the ⁡ outside of the subscript...

edemaine on 3 Dec 2018

👍1

We could also do some sanity checking out the MathML nodes we're outputting to make sure we're conforming to things like expected child count.

kevinbarabash on 3 Dec 2018