I suggest going and reading up a bit more about regex rather than asking such a basic question.
As most of you know, “^”sign is the start of the regular expression and “$” represent the end of the regular expression.
And there are three repeated expressions like “([a-ceghj-npr-tv-z])[0-9]”.
A postcode consists of various parts, from the area (the initial letters, corresponding to 121 divisions of the UK) to the unit (the entire postcode).
The get Area, get District, get Sector, and get Unit functions can be used to access these parts.
The goal is to teach you some basic HTML form elements and how their data is accessible to you in your PHP scripts.