Shorthand Actionscript

1

Probably a really easy question, but I’ve been having a hard time research it. I’ve noticed in some examples, people using shorthand actionscript. I’m just curious as to what it translates to and what are some good sources to find more shorthand actionscript. Below is an example that I would really like to know what it means. (what is the dollarsign/questionmark/colon for)

Thanx


XN.start = function ( _delay, _step, _startNum, _stopNum, _loop ) {
    this.$delay = ( _delay ? _delay : this.$delay );
    this.$step = ( _step ? _step : this.$step );
    this.$startNum = ( _startNum ? _startNum : 0 );
    this.$stopNum = ( _stopNum !== undefined ? _stopNum : this.$stopNum );
    this.$counter = this.$startNum;
    this.$loop = _loop;
    this.stop ();
    this.$count ();
};