wagtail/wagtailadmin/views/pages.py
def preview_loading(request):
    """
    This page is blank, but must be real HTML so its DOM can be written to once the preview of the page has rendered
    """
    return HttpResponse("<html><head><title></title></head><body></body></html>")

    This page is blank, but must be real HTML so its DOM can be written to once the preview of the page has rendered
    
This page is blank, but must be real HTML so its DOM can be written to once the preview of the page has rendered
This page is blank but must be real HTML so its DOM can be written to once the preview of the page has rendered
def preview_loading(request):
    return HttpResponse("<html><head><title></title></head><body></body></html>")
def preview_loading ( request ) : return HttpResponse ( "<html><head><title></title></head><body></body></html>" )
This page is blank, but must be real HTML so its DOM can be written to once the preview of the page has rendered
This page is blank but must be real HTML so its DOM can be written to once the preview of the page has rendered
"""
    This page is blank, but must be real HTML so its DOM can be written to once the preview of the page has rendered
    """
request