Park, Kyunghee, He Li, and Nan Luo. “Key Issues on Informal Learning in the 21st Century: A Text Mining-Based Literature Review”. International Journal of Emerging Technologies in Learning (iJET) 16, no. 17 (September 6, 2021): pp. 4–18. Accessed March 28, 2024. https://online-journals.org/index.php/i-jet/article/view/23663.