'First-class space' refers to the idea that space should be considered a first-class citizen. Space isn't just a by-product of components, it's something that requires consideration as it exists on the same level as component design.
Space is something that goes between components - it is not tied to individual components.
Components have an internal amount of space they require, i.e. their width and their height. However they don't naturally have a prescribed amount of external space they require (e.g. margin). As components can be used in various ways, space is contextual and relative to what's on the page.
This mindset is a lot closer to the gap property of CSS, and avoids having to deal with :last-child rules and similar.
[[20200314214239-layout-components]] [[20200402104023-components-margin]]