可以在http://

<input type="url" 
  name="url"
  id="url"
  placeholder="https://example.com"
  pattern="[Hh][Tt][Tt][Pp][Ss]?:\/\/(?:(?:[a-zA-Z\u00a1-\uffff0-9]+-?)*[a-zA-Z\u00a1-\uffff0-9]+)(?:\.(?:[a-zA-Z\u00a1-\uffff0-9]+-?)*[a-zA-Z\u00a1-\uffff0-9]+)*(?:\.(?:[a-zA-Z\u00a1-\uffff]{2,}))(?::\d{2,5})?(?:\/[^\s]*)?"
  required>

扩展

 [Hh] [Tt] [Tt] [Pp] [Ss]? :\/\/
 (?:
      (?: [a-zA-Z\u00a1-\uffff0-9]+ -? )*
      [a-zA-Z\u00a1-\uffff0-9]+ 
 )
 (?:
      \. 
      (?: [a-zA-Z\u00a1-\uffff0-9]+ -? )*
      [a-zA-Z\u00a1-\uffff0-9]+ 
 )*
 (?:
      \. 
      (?: [a-zA-Z\u00a1-\uffff]{2,} )
 )
 (?: : \d{2,5} )?
 (?: \/ [^\s]* )?