The AS3 text field has two properties, text and htmlText. The text property can be used to display purely plain text, even if it looks like html. The two properties are automatically linked by Flash, so editing text will update htmlText and vice-versa.
You should be able to use the text property to achieve your goal. Unfortunately, if you are using a style sheet with your text field, both properties will be treated as HTML. In this case, you have two choices. You can perform the styling without a style sheet, using simple TextFormat objects, which may be simple if your stylesheet is not too complex. If you really need to use a stylesheet, you can take advantage of AS3's link between the two text properties to escape your text automatically.
For example, if you wanted to update a text field called tf which uses a style sheet, but you wanted plain text, you could do it like this:
var temp:TextField = new TextField();
temp.text = plainText;
tf.text = temp.htmlText;
The temporary text field will automatically generate escaped HTML, which you can then use in your actual text field.
TextFieldwhich is a native Flash player class (not Flex), but it looks like you are using Flex. The TextField class has anhtmlTextproperty, so my assumption was that it only rendered HTML if you used that property, and that you would get your desired effect simply by using TextField'stextproperty. - Sunil D.