Currently all the box-alignment features are hidden under their respective contexts.
The css.properties.align-self.position_absolute_context key is in the absolute positioning feature, and same with flexbox/grid/etc. Only "align-content in block layouts" has it's own data visible.

The most immediate problem with this is that we can't see the multi-browser support that exists for alignment in absolute positioning. At the very least, position_absolute_context alignment keys deserves to be a feature.

At a high level, I think we lose out by not treating "box alignment" as a top level feature of CSS. I know it's historically been taught as 'part of' different layout systems - but authors have consistently found that confusing. The reality is we're close to having it everywhere, with a unified syntax we can teach and use across layouts.