Flash MX 2004.
text.lineType
Property; a string that sets the line type. Acceptable values are "single line", "multiline", "multiline no wrap", and "password".
This property works only with dynamic or input text and generates a warning if used with static text. The "password" value works only for input text.
The following example sets the lineType property to the value multiline no wrap:
fl.getDocumentDOM().selection[0].lineType = "multiline no wrap";