lib/index.js
function parseOptions (opts) {
  return removeEmpty({
    plugins: convertFn.call(this, opts.plugins),
    locals: convertFn.call(this, opts.locals),
    filename: convertFn.call(this, opts.filename),
    parserOptions: convertFn.call(this, opts.parserOptions),
    generatorOptions: convertFn.call(this, opts.generatorOptions),
    runtime: convertFn.call(this, opts.runtime),
    parser: convertFnSpecial.call(this, opts.parser),
    multi: convertFn.call(this, opts.multi)
  })
}
function parseOptions (opts) {
  return removeEmpty({
    plugins: convertFn.call(this, opts.plugins),
    locals: convertFn.call(this, opts.locals),
    filename: convertFn.call(this, opts.filename),
    parserOptions: convertFn.call(this, opts.parserOptions),
    generatorOptions: convertFn.call(this, opts.generatorOptions),
    runtime: convertFn.call(this, opts.runtime),
    parser: convertFnSpecial.call(this, opts.parser),
    multi: convertFn.call(this, opts.multi)
  })
}
Allows any option to be passed as a function which gets webpack's context as its first argument, in case some info from the loader context is necessary