angular/packages/compiler-cli/private/README.md

This is a directory defining the @angular/compiler-cli/private entry-point. The entry-point can be used to expose code that is needed by other Angular framework packages, without having to expose code through the primary entry-point.

The primary entry-point has a couple of downsides when it comes to cross-package imports:

• It exports various other things that will end up creating additional type dependencies. e.g. when the Angular localize package relies on it, it might end up accidentally relying on @types/node.
• The primary entry-point has a larger build graph, slowing down local development as much more things can invalidate the dependent targets. A smaller subset leads to faster incremental builds.