Fetch work item search results: usage of top and changedDate

Hey there,
am trying to find matches for some keywords with fetch_work_item_search_results. Param top within WorkItemSearchRequest is limited to max. 1000, does this mean they're max. 1000 results that can be returned or max. 1000 work items that are even checked?
I'd also like to apply a filter to check only for the work items from the past week, but when adding the filter with System.ChangedDate following exception is thrown:
azure.devops.exceptions.AzureDevOpsServiceError: Unknown filter [System.ChangedDate] found.. Which filter could be used instead or is there no possibility to filter a specific timeframe without using WIQL?

sort_option = SortOption(field='system.id', sort_order='ASC')
for keyword in test_keywords:
    search_request = WorkItemSearchRequest(
        #filters = { 'System.ChangedDate': [ '@Today-7' ]},
        search_text = keyword,
        order_by = [sort_option],
        skip = 0, 
        top = 1000, 
        include_facets = False
    )
    work_item_search_response = search_client.fetch_work_item_search_results(search_request, project=project_name)

Issue に示されている WorkItemSearchRequest と fetch_work_item_search_results のエントリーポイントから始め、Azure DevOps work item search API のドキュメントで top の上限とサポートされているフィルターを確認します。完了条件は、top が返されるアイテムを制限するのか検索対象のアイテムを制限するのかを文書化し、変更日で結果を制限するサポートされた方法を特定すること、または WIQL が必要であることを明確に記載することです。