foo – syntax of local-replacing hint.

0, semantics.
0.0, level-entity: notify the runtime to try the local-replacing as much as possible.
0.1, level-reference: level-entity + save the result to the same reference – it looks like performing an update.

1, syntax.
1.0, level-entity-func: (&func …)
1.0.0, (impl this …) => (&impl this …)
1.0.1, (impl stmt …) => (&impl stmt …) – reasonable?
1.0.2, (impl ref …) => (impl ref …)
1.0.3, (&impl ref …) => (&impl ref …)

1.1, level-entity-pkg: (&pkg:method …)
1.1.0, (this:method …) => (&this:method …)
1.1.1, (stmt:method …) => (&stmt:method …) – reasonable?
1.1.2, (ref:method …) => (ref:method …)
1.1.3, (&ref:method …) => (&ref:method …)

1.2, level-reference-func: ($func target) => (decl target (&func target))
1.2.0, ‘target’ must be a reference.

1.3, level-reference-pkg: ($pkg:method …) => (decl pkg (&pkg:method …))
1.3.0, ‘pkg’ must be a reference.