This is repeated between the second and third grouping of numbers, and we check for 3 consecutive digits then four consecutive digits to end it.
For example, you may want to ensure that someone inserts a valid e-mail address into a text box, or perhaps you want to ensure that someone fills in certain fields.
It's just that the input also includes the extra characters.
You included '^' to signify the beginning of line, but (as Andy said) you should include '$' to signify the end of line.
Unfortunately, intl-tel-input doesn't provide an event or callback that is executed after choosing a country.
The parenthesis are optional in your regexp, so you can have one but not the second.
Microsoft® Office Front Page® 2003 allows you to create some custom validation within the form feature.