This feature does not exist on Text. TextAttributes I am aware of includes: underlined, italic, bold, narrow, struck out, indents, text color, fonts (fonts work poorly in some circumstances) and alignment properties. Additional things such as links and URL are there but I have never achieved to make them work.
However, highlighting is available directly in PluggableTextMorph.
If you inspect a NautilusWindow (open Nautilus, use Morph halo to inspect it), you can have in the iv model the packageTreeNautilusUI, then in the iv sourceCodeArea a PluggableTextMorphWithLimits. Then in the inspector you can do:
highlights add:��
((TextHighlight on: self)
color: Color lightBlue;
lineRange: (10 to: 30))
After moving once the window, you'll notice this result:
So to have highlighting for your text I guess you'll have to dig in that direction ... This is directly implemented on the Morph and not on the Text so it may be a bit difficult to use.
Regards.
Cl��ment