suppress errors about multiple sub/superscripts?

[hbghlyj]

Is your feature request related to a problem? Please describe. Similar question to Is there a way to override LaTeX's errors about double subscripts and superscripts?

When one writes

a^b^c, a_b_c

or

a^b'

MathJax gives an error message complaining about multiple super/subscripts.

Is there a way to override the error and have MathJax output

a^{bc} a_{bc} {a^b}'  

Describe the solution you'd like Is there a way to redefine ^ and _ to append an empty {}? like in LaTeX:

\catcode`\^ = 13 \def^#1{\sp{#1}{}}
\catcode`\_ = 13 \def_#1{\sb{#1}{}}

[dpvc]

It can be done using the following configuration:

MathJax = {
  tex: {
    packages: {'[+]': ['my-scripts']}
  },
  startup: {
    ready() {
      const {Configuration} = MathJax._.input.tex.Configuration;
      const {CommandMap, MacroMap} = MathJax._.input.tex.SymbolMap;
      const BaseMethods = MathJax._.input.tex.base.BaseMethods.default;
      
      new MacroMap('my-script-chars', {
        '^': ['Macro', '\\sp{#1}{}', 1],
        '_': ['Macro', '\\sb{#1}{}', 1],
        '\'': 'Prime',
      }, {
        Macro: BaseMethods.Macro,
        Prime(parser, c) {
          const top = parser.stack.Top()
          const [base, atom] = top?.Peek(2) || [];
          if (base && atom && 
              base.isKind('msubsup') && !base.isKind('msup') && !!base.childNodes[base.sup] &&
              atom.isKind('TeXAtom') && atom.childNodes[0].childNodes.length === 0) {
            top.Pop(); top.Pop();
            const msup = parser.create('node', 'msup', [base.childNodes[0], base.childNodes[base.sup]]);
            parser.stack.Push(msup);
          }
          BaseMethods.Prime(parser, c);
        }
      });
      
      new CommandMap('my-script-cs', {
        sp: 'Superscript',
        sb: 'Subscript'
      }, BaseMethods);
      
      Configuration.create('my-scripts', {
        handler: {
          macro: ['my-script-cs'],
          character: ['my-script-chars']
        }
      });
      MathJax.startup.defaultReady();
    }
  }
}

Note, however, that a^b^c doesn't actually give a^{bc} but rather a^{b}{}^{c}{}, which is semantically different, though visually similar, so people with screen readers will get a strange result from this. Similarly for a_b_c, which gives a_{b}{}_{c}.

In actual TeX, these do not render quite the same:

(note the extra space in the second form). MathJax v3 gets this wrong and both appear identical, but v4 fixes the error and produces the result shown above. There is a similar extra space for the subscripts (in LaTeX and v4), and in the result for {a^b}' that is missing in v3.