What is it ?

This customfield allows to check that typed value respects an Regular Expression. By example, you will be able to validate that the value follows :

• A Currency format,
• A Date format
• A Delay format,
• or any other wanted format

How to configure it ?

Add a new Customfield and select the RegExp Customfields 

Go to Configure

Edit the Pattern of the Regular Expression 

and specify the Regular Expression

How the validation is processed ?

When the value is entered, it is controlled against the Regular Expression on Client side, before the validation of the screen.

and validation it blocked ...