Validating CustomPress custom fields

There’s a custom field created with CustomPress with field type “Text Box”. It has to be validated against http:// / https:// prefixes so it must be sure that there’s an URL put in that field and it does contain one of these two prefixes.

This two regular expressions had been tried in CustomPress “Regular Expression Validation” field for that custom field and none of them works:




How to validate that field using regular expression in CustomPress field setting?