internal/core/walk: Clarify Visitor.Before documentation

Signed-off-by: Matthew Sackman <matthew@cue.works>
Change-Id: I8ee9f023e391308506500ce6d556c07942a58d02
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198552
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

internal/core/walk/walk.go

@@ -35,9 +35,9 @@ type Visitor struct {
 	// Feature is invoked for all field names.
 	Feature func(f adt.Feature, src adt.Node)
 
-	// Before is invoked for all invoked for all nodes in pre-order traversal.
-	// Return false prevents the visitor from visiting the nodes descendant
-	// elements.
+	// Before is invoked for all nodes in pre-order traversal.
+	// Returning false prevents the visitor from visiting the node's
+	// children.
 	Before func(adt.Node) bool
 }