I am baffled by this function, which is called prior to this with parameters 22 and 58 for xVal ad yVal respectively. It doesn't display anything when the swf is compiled and tested, and it's error free. The code is in the document class:
private function mLine(xVal : int, yVal : int) {
var rCol = 0x0000FF;
var incr = Math.round((Math.random() * 20) + 8);
lns.push(new Shape());
var i = lns.length - 1;
this.addChild(lns[i]);
lns[i].graphics.moveTo(xVal, yVal);
lns[i].graphics.lineStyle(10, rCol);
lns[i].graphics.lineTo(xVal, yVal + 20);
lns[i].name = incr;
trace("lns[" + i + "] x is " + lns[i].x); // outputs 'lns[0] x is 0'
trace("xVal is " + xVal); // outputs 'xVal is 22'
trace("yVal is " + yVal); //outputs 'yVal is 58'
trace(stage.contains(lns[i])); // outputs 'true'
}
Assuming you have declared private var lns = []; somewhere, it draws a blue line (20px straight down from the given position).
It doesn't display anything
That means you probably don't have an object of that class on the stage. In your document class, you should use addChild to display an instance of the class containing mLine. mLine needs to be called somehow obviously. You could do this in the class' constructor, but you'd need to remove the last trace statement to avoid a null pointer error, because stage would be null then.
Edit: Missed that you said it is in the Document class. So, try and see if drawing anything else works. The problem doesn't seem to be with this function.