Per the manual the * make the field in QWizardPage manadory, i.e. the button "Next" enables only when that field is filled.

I do:

registerField("field*", lineEdit);

and that works fine with QLineEdit but the same thing doesn't fly with QTextEdit. I do:

registerField("field*", textEdit, "plainText");

(I have to add "plainText" since textEdit is not a default property of QWizardPage)
and that doesn't work - the button "Next" does not get enabled when that textEdit gets filled.
I've tried:

registerField("field*", textEdit, "plainText", "textChanged");

didn't help either...