What is the 'nine-dash line' and what does it have to do with the Barbie movie?

Vietnam's response to the Barbie movie's depiction of the South China Sea shows how sensitive these matters are in South-East Asia - and especially in Vietnam. Since the late 1940s, China has promoted the so-called nine-dash line in the South China Sea. As depicted in various official and unofficial Chinese maps, the line extends off the coast of China's Hainan Island, and runs close to the coast of Vietnam, deep into the South China Sea, enclosing the Spratly Islands. In addition to China continuously advancing its position regarding the legitimacy of the nine-dash line, countries including Australia, France, Indonesia, Malaysia, New Zealand, the Philippines, United Kingdom, and Vietnam have rebutted China's assertions. While the Philippines conclusively won the legal argument that the nine-dash line had no basis in modern international law or the law of the sea, China refused to respect the outcome of that case and continues to assert its South China Sea entitlements. Vietnam's response to Hollywood's depiction of China's nine-dash line is understandable. It demonstrates a fierce resistance to any legitimacy that China's ongoing South China Sea nine-dash line claims may generate, even in Barbie's fictional world.