Unable to add Textrun element to Title in Word2007

[CyferZ]

This is a fairly straightforward issue, the title describes what I'm encountering and it's quite easy to replicate.

When creating a TextRun element in a Word document, I am unable to do this:

$section->addTitle($textRun, 3);

The error I encounter is:
TypeError XMLWriter::text(): Argument #1 ($content) must be of type string, PhpOffice\PhpWord\Element\TextRun given.

How I tried adding a TextRun in my Word document:

$exampleTextRun = new \PhpOffice\PhpWord\Element\TextRun();
$exampleTextRun->addText("Title ", 'fontSize9');
$exampleTextRun->addText("colour", ['color' => 'DD0000']);

$section->addTitle($exampleTextRun, 2);