begingroup

The begingroup extension implements commands that provide a mechanism for localizing macro definitions so that they are not permanent. This is useful if you have a blog site, for example, and want to isolate changes that your readers make in their comments so that they don’t affect later comments.

It defines two new non-standard macros, \begingroup and \endgroup, that are used to start and stop a local namespace for macros. Any macros that are defined between the \begingroup and \endgroup will be removed after the \endgroup is executed. For example, if you put \(\begingroup\) at the top of each reader’s comments and \(\endgroup\) at the end, then any macros they define within their response will be removed after it is processed. Note that \begingroup and \endgroup do not have to appear within the same expression.

In addition to these two macros, the begingroup extension defines the standard \global and \gdef control sequences from TeX. (The \let, \def, \newcommand, and \newenvironment control sequences are already defined in the newcommand package.)

The begingroup package also defines two non-standard macros: \begingroupReset and \begingroupSandbox. The first effectively applies \endgroup to any open \begingroup macros, returning the definitions to the ones that were in effect before the first \begingroup, plus any new \global definitions.

The \begingroupSandbox macro can be used to isolate the definitions in one section of the page from those in another, so that sites, such as question-and-anser sites, can use this between user posts to make sure that one user’s definitions won’t affect any other user’s expressions. The \begingroupSandbox macro can’t be redefined, and its action is to remove all the open \begingroup calls and then start a new local greoup (effectively doing \begingroupReset\begingroup). This removes any previous user definitions and makes a new group for the next user’s definition. Furthermore, \global definitions are put into the new \begingroup so that even if the math includes \global definitions, they will be removed when the next \begingroupSandbox command is performed, and will not pollute the next user’s macro namespace.

Any definitions made before the first \begingroupSandbox invocation is made will be available within all the sandboxes, but once \begingroupSandbox is performed, there is no going back; the original macro namespace is no longer accessible to new definitions.

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The begingroup package is not autoloaded, so you must request it explicitly if you want to use it. To load the begingroup extension explicitly, add '[tex]/begingroup' to the load array of the loader block of your MathJax configuration, and add 'begingroup' to the packages array of the tex block.

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

Alternatively, use \require{begingroup} in a TeX expression to load it dynamically from within the math on the page, if the require extension is loaded.

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begingroup Options

Adding the begingroup extension to the packages array defines an begingroup sub-block of the tex configuration block with the following values:

MathJax = {
  tex: {
    begingroup: {
      allowGlobal: ["let", "def", "newcommand", "DeclareMathOperator", "Newextarrow"]
    }
  }
};

allowGlobal: ["let", "def", "newcommand", "DeclareMathOperator", "Newextarrow"]

This lists the commands that can follow the \global command. Extensions may add to this if they include new macros that can define global values. Alternatively, you can remove commands from the list to prevent users from making global definitions.

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begingroup Commands

The begingroup extension implements the following macros: \begingroup, \begingroupReset, \begingroupSandbox, \endgroup, \gdef, \global

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