This page describes the text type with the renderType='t3editor'.

// ...
'type' => 'text',
'renderType' => 't3editor',
// ...

The renderType = 't3editor' triggers a code highlighter if extension t3editor is loaded, otherwise falls back to "default" renderType.

System extension "t3editor" provides an enhanced textarea for TypoScript input, with not only syntax highlighting but also auto-complete suggestions. Beyond that the "t3editor" extension makes it possible to add syntax highlighting to textarea fields, for several languages.