Using breakParent to force a linebreak - prettier

Question

I'm working on a prettier plugin and am struggling to understand the breakParent command.
From the command documentation:
Include this anywhere to force all parent groups to break.
The documentation is quite sparse, so maybe I've just completely misunderstood what it's supposed to do, but my expectation would be that it will line break parent groups in exactly the same way they would have if the line exceeded the maximum width.
I would therefore have expected the following commands
{
type: 'group',
contents: {
type: 'concat',
parts: [
'<div>',
{
type: 'indent',
contents: {
type: 'concat',
parts: [{ type: 'line', soft: true }, 'Text', { type: 'break-parent' }],
},
},
{ type: 'line', soft: true },
'</div>',
],
},
}
to print
<div>
Text
</div>
but instead I get
<div>Text</div>
How do I achieve what I thought breakParent would do, i.e. force the surrounding code to line break from inside the group?
And if that's not possible, what does breakParent actually do?
(Obviously, it can be done by turning the soft lines into hard lines, but that's not the solution I'm looking for because only the code generating "Text" in the example above knows if a line break is needed or not)