Answer
For a custom field specifically, select 'markdowneditor' as the control type in Page Designer — this gives the field a proper rich-text/formatted editing experience (with a formatting toolbar), rather than the plain-text box a standard string-type custom field normally gets. This is the way to offer formatted, maintainable content (like notes connected to a part) directly in Aurena, without the character-limit and no-formatting constraints of a basic multiline text field.