How to use title of the parent page as default value of a text field?

How can i define the Title of the Parent Page as default-value of a text field of a new created page?

trying this doesn’t work:

fieldname:
  type: text
  default: " {{ page.parent.title }}"

Query language doesn’t work for default values (in most cases). You would have to create a new field type based on the text field with support for query language, similar to the example here ( :walking_woman:)