Funnily, CSS flexbox and grid models can be seen as a kind of constraint layout system. Penpot, the Figma competitor, has even implemented a flexbox subset as i

Funnily, CSS flexbox and grid models can be seen as a kind of constraint layout system. Penpot, the Figma competitor, has even implemented a flexbox subset as its layout mechanism. The moral of the story, if there's one, is that constraints may be useful if they reflect common design rules and the system is built around those cases with high level abstractions, but simply allowing any possible low-level constraint may be too complex for the case of designing GUIs.