I just came across a situation in which it would be an elegant solution to have only portions of a text area (previously loaded with text) be editable while other portions a
Interesting idea, but sadly, the text within the text area must be treated uniformly, i.e. you can't disable a subsection of the text area contents.
You do have options, however. If you can identify the text that needs to be disabled, you can add it as a DOM element (i.e. a div), and then position it in a way that implies it is inside the text area.
You can imply that this div is inside the text area either by making the text area big and using position: relative/absolute styles to move the div over the text area. Or, you can remove the border on the text area and put it on a container that also contains the div w/ "disabled" text.