what's (page = DEFAULT_PAGE) role in CustomPagination by DRF (django-rest-framework)?

For some reason, I could not understand the meaning and role of page=DEFAULT_PAGE in Custom Pagination in the DRF topic. Can you explain its role to me in the code below?

Consider - pagination.py:

from rest_framework.pagination import PageNumberPagination
from rest_framework.response import Response


DEFAULT_PAGE = 9
DEFAULT_PAGE_SIZE = 9

class CustomPagination(PageNumberPagination):
    page = DEFAULT_PAGE
    page_size = DEFAULT_PAGE_SIZE
    page_size_query_param = 'page_size'

    def get_paginated_response(self, data):
        return Response({
            'links': {
                'next': self.get_next_link(),
                'previous': self.get_previous_link()
            },
            'total': self.page.paginator.count,
            'page': int(self.request.GET.get('page', DEFAULT_PAGE)), # can not set default = self.page
            'page_size': int(self.request.GET.get('page_size', self.page_size)),
            'results': data
        })

Note : This is important to me for setting up my app and I wanted to understand its role... Although I consulted the documentation, I didn't understand much about the role of page=PAGE_DEFAULT.

The setting page = DEFAULT_PAGE define a default page number (9 in your example) for the DRF custom pagination class. When the client doesn't specify one in the request, it ensures a fallback for pagination.