public class TextStylesheetExample extends Sprite {
    var myLabel:TextField = new TextField();
    var labelText:String = "Hello world.";
    var newStyle:StyleSheet = new StyleSheet();

    public function TextStylesheetExample()
    {
        var styleObj:Object = new Object();
        styleObj.fontWeight = "bold";
        styleObj.color = "#660066";
        newStyle.setStyle(".defStyle", styleObj);

        myLabel.styleSheet=newStyle;
        myLabel.htmlText=labelText;
        addChild(myLabel);
    }
}

var labelText:String = "<p>Hello world.</p>";
...
newStyle.setStyle("p", styleObj);

var tf:TextField = new TextField();
tf.text = "hello world";
trace(tf.htmlText);