10.4.4 Extensions
It is common to see Static Extension used with the math library.  This code shows a simple example:
class MathStaticExtension {
  /* Converts an angle in radians to degrees */
  inline public static function toDegrees(radians:Float):Float {
    return radians * 180 / Math.PI;
  }
}
using MathStaticExtension;
class Main {
  public static function main() {
    var ang = 1/2*Math.PI;
    trace(ang.toDegrees()); //90
  }
}