function validateOption(options, name, values) {
  if (options[name] !== undefined && !contains(values, options[name])) {
    var index = findIndex(values, options[name]);

    if (index !== -1) {
      // right value, wrong casing
      // TODO: lower case values are deprecated since v3, remove this warning some day.
      console.warn('Warning: Wrong casing for configuration option "' + name + '", should be "' + values[index] + '" instead of "' + options[name] + '".');
      options[name] = values[index]; // change the option to the right casing
    } else {
      // unknown value
      console.warn('Warning: Unknown value "' + options[name] + '" for configuration option "' + name + '". Available options: ' + values.map(JSON.stringify).join(', ') + '.');
    }
  }
}
Validate an option
@param {Object} options         Object with options
@param {string} name            Name of the option to validate
@param {Array.<string>} values  Array with valid values for this option