Add editor to modular page form

I am using the antimatter theme to get my head round Grav. What I’m trying to do is change the textbox on the features modular page template into the markdown editor.

If I go to antimatter/blueprints/modular/features.yaml and edit:
.text:
type: text
label: Text

to be:
.text:
type: editor
label: Text

The markdown editor displays but it acts as a textarea ie: mardown syntax is rendered as raw text and html renders as html.

I also tried:
.text:
type: markdown
label: Text

The result is the same as editor?

What am I missing? Thanks for any help.