SI-2458 Clarify spec for package syms (scala#5151)

Package definitions are priority 4.

Update the big example to be cut/pastable.

spec/02-identifiers-names-and-scopes.md

@@ -17,12 +17,12 @@ which are collectively called _bindings_.
 Bindings of different kinds have a precedence defined on them:
 
 1. Definitions and declarations that are local, inherited, or made
-   available by a package clause in the same compilation unit where the
-   definition occurs have highest precedence.
+   available by a package clause and also defined in the same compilation unit
+   as the reference, have highest precedence.
 1. Explicit imports have next highest precedence.
 1. Wildcard imports  have next highest precedence.
-1. Definitions made available by a package clause not in the
-   compilation unit where the definition occurs have lowest precedence.
+1. Definitions made available by a package clause, but not also defined in the
+   same compilation unit as the reference, have lowest precedence.
 
 There are two different name spaces, one for [types](03-types.html#types)
 and one for [terms](06-expressions.html#expressions). The same name may designate a
@@ -34,22 +34,18 @@ in some inner scope _shadows_ bindings of lower precedence in the
 same scope as well as bindings of the same or lower precedence in outer
 scopes.
 
-<!-- TODO: either the example, the spec, or the compiler is wrong
-
-Note that shadowing is only a partial order. In a situation like
+Note that shadowing is only a partial order. In the following example,
+neither binding of `x` shadows the other. Consequently, the
+reference to `x` in the last line of the block is ambiguous.
 
 ```scala
 val x = 1
-{
-  import p.x
+locally {
+  import p.X.x
   x
 }
 ```
 
-neither binding of `x` shadows the other. Consequently, the
-reference to `x` in the last line of the block above would be ambiguous.
--->
-
 A reference to an unqualified (type- or term-) identifier $x$ is bound
 by the unique binding, which
 
@@ -69,43 +65,64 @@ the member of the type $T$ of $e$ which has the name $x$ in the same
 namespace as the identifier. It is an error if $T$ is not a [value type](03-types.html#value-types).
 The type of $e.x$ is the member type of the referenced entity in $T$.
 
+Binding precedence implies that the way source is bundled in files affects name resolution.
+In particular, imported names have higher precedence than names, defined in other files,
+that might otherwise be visible because they are defined in
+either the current package or an enclosing package.
+
+Note that a package definition is taken as lowest precedence, since packages
+are open and can be defined across arbitrary compilation units.
+
+```scala
+package util {
+  import scala.util
+  class Random
+  object Test extends App {
+    println(new util.Random)  // scala.util.Random
+  }
+}
+```
+
 ###### Example
 
-Assume the following two definitions of objects named `X` in packages `P` and `Q`.
+Assume the following two definitions of objects named `X` in packages `p` and `q`
+in separate compilation units.
 
 ```scala
-package P {
+package p {
   object X { val x = 1; val y = 2 }
 }
 
-package Q {
-  object X { val x = true; val y = "" }
+package q {
+  object X { val x = true; val y = false }
 }
 ```
 
 The following program illustrates different kinds of bindings and
 precedences between them.
 
 ```scala
-package P {                  // `X' bound by package clause
-import Console._             // `println' bound by wildcard import
-object A {
-  println("L4: "+X)          // `X' refers to `P.X' here
-  object B {
-    import Q._               // `X' bound by wildcard import
-    println("L7: "+X)        // `X' refers to `Q.X' here
-    import X._               // `x' and `y' bound by wildcard import
-    println("L8: "+x)        // `x' refers to `Q.X.x' here
-    object C {
-      val x = 3              // `x' bound by local definition
-      println("L12: "+x)     // `x' refers to constant `3' here
-      { import Q.X._         // `x' and `y' bound by wildcard import
-//      println("L14: "+x)   // reference to `x' is ambiguous here
-        import X.y           // `y' bound by explicit import
-        println("L16: "+y)   // `y' refers to `Q.X.y' here
-        { val x = "abc"      // `x' bound by local definition
-          import P.X._       // `x' and `y' bound by wildcard import
-//        println("L19: "+y) // reference to `y' is ambiguous here
-          println("L20: "+x) // `x' refers to string "abc" here
+package p {                   // `X' bound by package clause
+import Console._              // `println' bound by wildcard import
+object Y {
+  println(s"L4: $X")          // `X' refers to `p.X' here
+  locally {
+    import q._                // `X' bound by wildcard import
+    println(s"L7: $X")        // `X' refers to `q.X' here
+    import X._                // `x' and `y' bound by wildcard import
+    println(s"L9: $x")        // `x' refers to `q.X.x' here
+    locally {
+      val x = 3               // `x' bound by local definition
+      println(s"L12: $x")     // `x' refers to constant `3' here
+      locally {
+        import q.X._          // `x' and `y' bound by wildcard import
+//      println(s"L15: $x")   // reference to `x' is ambiguous here
+        import X.y            // `y' bound by explicit import
+        println(s"L17: $y")   // `y' refers to `q.X.y' here
+        locally {
+          val x = "abc"       // `x' bound by local definition
+          import p.X._        // `x' and `y' bound by wildcard import
+//        println(s"L21: $y") // reference to `y' is ambiguous here
+          println(s"L22: $x") // `x' refers to string "abc" here
 }}}}}}
 ```