Hi Guilherme,
Great question, as the flag doesn't really give enough away!
If you add regex to the Format Expression field, it's always "strict" in its application. Only adding soft validation would allow a user to select a value that doesn't conform to the expression. (There's a great update to this in 2.2 that allows the user to configure its behaviour in more detail)
The Strict Regex flag is designed to be used when you are seeking a unique value that can appear anywhere in the document, and there's no other way to consistently identify it. i.e. There are no consistent keyworks or headers in its vicinity.
So if you had a document with an account number, but it could appear anyway on the page, it has nothing to indicate what it is and can only be recognised by it's format. Then complete the Format Expression field and check the Strict Regex flag, leave Sample Headers and other fields blank.
Does that help?
Thanks
Ben
Ben Lyons
Principal Product Specialist - Decipher
SS&C Blue Prism
UK based