[spec] Specify when opApply's delegate returns nonzero (#3814)

* [spec] Specify when opApply's delegate returns nonzero and add example about `break`

Author: ntrel

spec/statement.dd

@@ -695,7 +695,7 @@ $(GNAME OpApplyParameter):
 )
 
     $(P where each $(I OpApplyParameter) of `dg` must match a $(GLINK ForeachType)
-        in a *ForeachStatement*,
+        in a $(GLINK ForeachStatement),
         otherwise the *ForeachStatement* will cause an error.)
 
     $(P Any *ForeachTypeAttribute* cannot be `enum`.)
@@ -738,13 +738,18 @@ $(GNAME OpApplyParameter):
         apply must return 0.)
     )
 
+    $(P The result of calling the delegate will be nonzero if the *ForeachStatement*
+        body executes a matching $(GLINK BreakStatement), $(GLINK ReturnStatement), or
+        $(GLINK GotoStatement) whose matching label is outside the *ForeachStatement*.
+    )
+
     $(P For example, consider a class that is a container for two elements:)
 
         $(SPEC_RUNNABLE_EXAMPLE_RUN
         --------------
         class Foo
         {
-            uint[2] array;
+            uint[] array;
 
             int opApply(scope int delegate(ref uint) dg)
             {
@@ -763,10 +768,13 @@ $(GNAME OpApplyParameter):
             import std.stdio;
 
             Foo a = new Foo();
-            a.array = [73, 82];
+            a.array = [73, 82, 2, 9];
 
             foreach (uint u; a)
             {
+                if (u < 5)
+                    break;
+
                 writeln(u);
             }
         }