LaTex rendering has alignment issues (v3 & v2)

[LonHon]

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Issue Summary

A summary of the issue and the browser/OS environment in which it occurs. If
suitable, include the steps required to reproduce the bug.

Steps to Reproduce:

Goto website https://jsbin.com/wiworocogi/1/edit?html,output and copy the following formula for rendering

LaTex:

 \style{font-family:Times New Roman}{{}_{12}^{234}Pu}


MathML
<math style="font-family: Times New Roman" ><mmultiscripts><mi>P</mi><mprescripts/><mn>12</mn><mn>234</mn></mmultiscripts><mi>u</mi></math>

Technical details:

• MathJax Version: 3.2
• Client OS: (e.g., Mac OS X 10.8.4)
• Browser: (e.g., Chrome 29.0.1547.57)

and loading MathJax via

<script src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script>

[dpvc]

MathJax's output is correct for the expression that you have entered (and it is the same as would be produced in actual LaTeX). When you write {}_{12}^{234}, you are creating an empty element that has a subscript and superscript. These are aligned on the left next to the empty base (just as they would be for x_{12}^{234} with a non-empty base). The fact that this is followed by Pu is immaterial to the layout. LaTeX does not have a semantic understanding of what you type, and its layout rules don't take the following Pu into account. The MathML that this construction produces is

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <msubsup>
    <mrow data-mjx-texclass="ORD"></mrow>
    <mrow data-mjx-texclass="ORD">
      <mn>12</mn>
    </mrow>
    <mrow data-mjx-texclass="ORD">
      <mn>234</mn>
    </mrow>
  </msubsup>
  <mi>P</mi>
  <mi>u</mi>
</math>

The MathML that you entered by hand is quite different, as it uses <mmultiscripts>, which does connect the prescripts to the base Pu, a wholly different structure from the LaTeX you used.

There are several ways you could get the result you are looking for. One would be to use

{}_{\phantom{0}12}^{234}Pu

to get the subscript to appear to be right justified (the numbers are all the same width in order to make such alignments possible in LaTeX).

Another would be to use the mhchem package to do

\ce{_{12}^{234}Pu}

which will right-justify the prescripts. This is probably the easiest solution.

Alternatively, you could use the \prescript macro from the mathtools package:

\prescript{234}{12}{Pu}

which will generate an mmultiscript structure like what you have used (and if you add postscripts, they will be included in the mmultiscript as postscripts as well).

In any case, this is not a bug in MathJax, or in LaTeX, as that is how both are intended to work.