Unmodified TeX has very few ways of preventing widows and orphans. In documents with figures, section headings, and equations, TeX can stretch the vertical glue between items in order to prevent widows and orphans, but many documents have no figures or headings. TeX can also shorten the page by 1 line, but this will give each page a different length which can make a document look uneven. The typical solution is to strategically insert \looseness=1, but this requires manual editing every time that the document is edited. Lua-widow-control is essentially an automation of the \looseness method: it uses Lua callbacks to find stretchy paragraphs, then it lengthens them to remove widows and orphans. Lua-widow-control is compatible with all LuaTeX and LuaMetaTeX-based formats.