Why is this an issue?

Sharing some naming conventions is a key point to make it possible for a team to efficiently collaborate. This rule allows to check that field names match a provided regular expression.

Noncompliant code example

With the default regular expression ^[_a-z][a-zA-Z0-9]*$:

class MyClass {
  public var my_field:int;
}

Compliant solution

public class MyClass {
   public var myField:int;
}