I have input in my form HTML, and i want to control the year typed must be in this form :  
 YYYY OR YYYY/YYYY/YYYY/YYYY/YYYY ...ect  

my pattern is : 

First test :

```
pattern="^((19)\d{2}\/|(20)[0-1][0-9]\/)+"

```

Second Test:

```
pattern="^((19)\d{2}\/?|(20)[0-1][0-9]\/?)+"

```

I expect for exemple 2018/2019/1999 but i must type 2018/2019/1999/ for the first test  

But if i test with the second:
this form is accepted but i don't want to be accepted : 20182019/1999