tree-overlay design: minor updates

- For the rule functions TREE_OVERLAY and DISJOINT_TREE_OVERLAY
  call the argument "$1", to align with the argument name for
  BLOB and TREE.
- For the built-in functions `"tree_overlay"` and `"disjoint_tree_overlay"`,
  align this the built-in function `"tree"` and allow staging of
  the resulting tree.

1 files changed, 3 insertions, 2 deletions

diff --git a/doc/future-designs/tree-overlay.md b/doc/future-designs/tree-overlay.md
index 7f809208..014c64f1 100644
--- a/doc/future-designs/tree-overlay.md
+++ b/doc/future-designs/tree-overlay.md
@@ -94,7 +94,7 @@ CAS in topological order, in order to keep the tree invariant.
 In the defining expressions of rules, two additional constructors
 `TREE_OVERLAY` and `DISJOINT_TREE_OVERLAY` are added that (like
 `ACTION`, `BLOB`, and `TREE`) can be used to describe parts of the
-action graph. These constructors have one argument `"deps"` which
+action graph. These constructors have one argument `"$1"` which
 has to evaluate to a list of tree-conflict—free mappings
 of strings to artifacts, also called "stages". The result of this
 function is a single artifact, the tree defined to be the overlay
@@ -122,4 +122,5 @@ rules `"tree_overlay"` and `"disjoint_tree_overlay"`. They have a
 single field `"deps"` which expects a list of targets. Both, runfiles
 and artifacts of the `"tree_overlay"` target are the tree overlays
 or conflict-free tree overlay, respectively, of the artifacts of
-the specified `"deps"` targets in the specified order.
+the specified `"deps"` targets in the specified order staged at the
+value of the field `"name"` which has to evaluate to a single string.