The document provided is a bibliography or list of references for a research paper or document on the topic of children's outdoor play spaces and environmental settings. It includes 18 different source references on this topic published between 1981-2017, including books, academic journals, conference proceedings, theses, and dissertations. The sources cited come from Indonesia, the United States, China, and Portugal and cover topics like children's perceptions of natural play spaces, the importance of outdoor play, characteristics of children's playground settings, and relationships between environmental settings and children's behaviors.