code: function strictMode (callback) {
    'use strict'
  
    // The module api is in *Locked* state, so it will not change
    // see http://nodejs.org/api/modules.html
    // that is why I just copyed and pasted the orig module wrapper.
    //
    // By the way, in test.js there is a test that checks if the content of
    // *origWrapper* needs an update.
  
    const origWrapper = '(function (exports, require, module, __filename, __dirname) { '
    const strictWrapper = origWrapper + '"use strict";'
  
    if (typeof callback !== 'function') {
      throw new TypeError('Argument *callback* must be a function')
    }
  
    const module = require('module')
  
    if (typeof module.wrapper === 'undefined') {
      // If you enter here, you are in a context other than server side Node.js.
      // Since module.wrapper is not defined, do not switch strict mode on.
      callback()
    } else {
      if (module.wrapper[0] === origWrapper) {
        module.wrapper[0] = strictWrapper
  
        // Every require in this callback will load modules in strict mode.
        try {
          callback()
        } catch (err) {
          console.error(err.stack)
        }
  
        // Restore orig module wrapper, play well with others.
        module.wrapper[0] = origWrapper
      } else {
        // If module.wrapper[0] changed, do not switch strict mode on.
        callback()
      }
    }
  }
docs: Wraps module `exports`
  
  See [Usage](http://g14n.info/strict-mode#usage)
  
  @param {Function} callback containing caller package's exports statements