css disable zoom on mobile

1<meta name='viewport' 
2     content='width=device-width, initial-scale=1.0, maximum-scale=1.0, 
3     user-scalable=0' >

1<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />

1<meta 
2     name='viewport' 
3     content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0' 
4/>

1<meta name="viewport" content="width=device-width, user-scalable=no">

1<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
2