tagFormat

The tagFormat extension provides the ability to customize the format of the equation tags and automatic equation numbers. You do this by providing functions in the tagFormat object of the tex block of your MathJax configuration. The functions you can provide are listed in the TagFormat Options section.

For example,

MathJax = {
  section: 1,
  tex: {
    tagFormat: {
      number: (n) => MathJax.config.section + '.' + n,
      id: (tag) => 'eqn-id-' + tag
    }
  },
  startup: {
    ready() {
      MathJax.startup.defaultReady();
      MathJax.startup.input[0].preFilters.add(({math}) => {
        if (math.inputData.recompile) {
          MathJax.config.section = math.inputData.recompile.section;
        }
      });
      MathJax.startup.input[0].postFilters.add(({math}) => {
        if (math.inputData.recompile) {
          math.inputData.recompile.section = MathJax.config.section;
        }
      });
    }
  }
};

arranges for automatic equation numbers to be of the form 1.n, and uses ids of the form eqn-id-1.n as the id attribute of the tags within the web page. It also sets up pre- and -post-filters for the TeX input jax that arrange for the section number to be properly handled for automatically numbered equations that contain forward references to later expressions. This example uses the modern function notation (using =>), but you could also use function (n) {return ...}.

You can adjust the section numnber using JavaScript by setting the MathJax.config.section variable. It is also possible to create TeX macros for controlling the section number. Here is one possibility:

MathJax = {
  startup: {
    ready() {
      const Configuration = MathJax._.input.tex.Configuration.Configuration;
      const CommandMap = MathJax._.input.tex.SymbolMap.CommandMap;
      new CommandMap('sections', {
        nextSection: 'NextSection',
        setSection: 'SetSection',
      }, {
        NextSection(parser, name) {
          MathJax.config.section++;
          parser.tags.counter = parser.tags.allCounter = 0;
        },
        SetSection(parser, name) {
          const n = parser.GetArgument(name);
          MathJax.config.section = parseInt(n);
        }
      });
      Configuration.create(
        'sections', {handler: {macro: ['sections']}}
      );
      MathJax.startup.defaultReady();
    }
  }
};

(Of course, you will want to merge this configuraiton in with the rest of your configuration options.)

This makes two new macros available: \nextSection, which increments the section counter, and \setSection{n}, which sets the section number to n. These must be issues within math delimiters in order for MathJax to process them. In order to prevent them from producing any output in your page, you could enclose them within a hidden element. For example,

<span style="display: hidden">\(\nextSection\)</span>

or something similar.

To load the tagFormat extension, add '[tex]/tagFormat' to the load array of the loader block of your MathJax configuration, and add 'tagFormat' to the packages array of the tex block.

window.MathJax = {
  loader: {load: ['[tex]/tagFormat']},
  tex: {packages: {'[+]': ['tagFormat']}}
};

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