Flash MX 2004.
textAttrs.leftMargin
Property; an integer that specifies the paragraph’s left margin. Acceptable values are 0 through 720.
The following example sets the leftMargin property of the selected text field from the character at index 2 up to, but not including, the character at index 8 to 100. This can affect characters outside the specified range if they are in the same paragraph.
fl.getDocumentDOM().selection[0].setTextAttr("leftMargin", 100, 2, 8);