Css subgrids (CSS Grid Layout Module Level 2) are useful to simplify complex layouts.
See for example:
https://rachelandrew.co.uk/archives/2017/07/20/why-display-contents-is-not-css-grid-layout-subgrid/ or https://wiki.selfhtml.org/wiki/CSS/Tutorials/Grid/Verschachtelte_Raster
Can similar behaviour be implemented as org.eclipse.swt.widgets.Layout for nested Composites?