text: 
  const ValidationError = require('../error/validation_error');
  const validateString = require('./validate_string');
  
  module.exports = function(options) {
      const value = options.value;
      const key = options.key;
  
      const errors = validateString(options);
      if (errors.length) return errors;
  
      if (value.indexOf('{fontstack}') === -1) {
          errors.push(new ValidationError(key, value, '"glyphs" url must include a "{fontstack}" token'));
      }
  
      if (value.indexOf('{range}') === -1) {
          errors.push(new ValidationError(key, value, '"glyphs" url must include a "{range}" token'));
      }
  
      return errors;
  };
  