code: func (eg *exampleGenerator) generateFormatExample() interface{} {
  	if !eg.hasFormatValidation() {
  		return nil
  	}
  	format := eg.a.Validation.Format
  	if res, ok := map[string]interface{}{
  		"email":     eg.r.faker.Email(),
  		"hostname":  eg.r.faker.DomainName() + "." + eg.r.faker.DomainSuffix(),
  		"date":      time.Unix(int64(eg.r.Int())%1454957045, 0).Format("2006-01-02"), // to obtain a "fixed" rand
  		"date-time": time.Unix(int64(eg.r.Int())%1454957045, 0).Format(time.RFC3339), // to obtain a "fixed" rand
  		"ipv4":      eg.r.faker.IPv4Address().String(),
  		"ipv6":      eg.r.faker.IPv6Address().String(),
  		"ip":        eg.r.faker.IPv4Address().String(),
  		"uri":       eg.r.faker.URL(),
  		"mac": func() string {
  			res, err := regen.Generate(`([0-9A-F]{2}-){5}[0-9A-F]{2}`)
  			if err != nil {
  				return "12-34-56-78-9A-BC"
  			}
  			return res
  		}(),
  		"cidr":    "192.168.100.14/24",
  		"regexp":  eg.r.faker.Characters(3) + ".*",
  		"rfc1123": time.Unix(int64(eg.r.Int())%1454957045, 0).Format(time.RFC1123), // to obtain a "fixed" rand
  	}[format]; ok {
  		return res
  	}
  	panic("Validation: unknown format '" + format + "'") // bug
  }
docs: // generateFormatExample returns a random example based on the format the user asks.