docs-source/lib/remote-include-processor.js

module.exports = function () {
  this.includeProcessor(function () {
    this.$option('position', '>>')
    this.handles((target) => target.startsWith('https://'))
    this.process((doc, reader, target, attrs) => {
      const contents = require('child_process').execFileSync('curl', ['--silent', '-L', target], { encoding: 'utf8' })
      reader.pushInclude(contents, target, target, 1, attrs)
    })
  })
}