What should I write inside regularExpression function?

Question

Screenshot image:
https://ibb.co/mvYLue

Answer 1

A regular expression to check the input with.

Check out, https://www.sololearn.com/learn/9704/?ref=app

Answer 2

Is there a description of the task anywhere?

Answer 3

i used it for alphanumeric values like for PAN no,email address.
For instance,
Example : Regular expression for an email address :
^([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$
The above regular expression can be used for checking if a given set of characters is an email address or not.