ActionScript 3.0 :: Change The Style Of Single Words In A Textfield?

I have a question about textfields and I'm wondering if it is possible to change text styles of single words or lines within a textfield with actionscript.

I use an empty textfield and add my text to that field in actionscript with the following code: myTfield.text = "insert text here"

the text contains multiple lines and I want some of them to be bold, italic or a bigger font size. The reason why I am adding my text to my textfield this way is because I need the text in the textfield to change when some buttons are pressed. Text will be added or removed from the textfield if buttons are pressed by the user and the current way I'm changing the text is by simply re-using the code above with new text in it. (it makes the code quite long though, but I guess I'll have to deal with that) But because I'm adding text this way I am not sure how to change the style of different parts of the text.

On a related note, with CS5 there are now a number of options for textfields. There is TLF text and classic text. I've searched around for the differences but I don't find the awnsers very clear. What option should I use for my textfield if I want it to look sharp like the text I'm typing here (its just regular text, no headers or anything). Some options just give blurry text because of the anti-alias and some settings don't seem to change a thing. And at times embedding fonts looks nice but sometimes it makes it worse. There are so many options to choose from, but it is unclear what would work best for regular text. (my text won't animate, it does move with a scrollbar, but I only care about how it looks when the scrollbar is still)