[spec/expression] Improve AssignExpression docs for arrays

Differentiate between an a slice expression and assigning to an array.
Rename 'Array Setting' to 'Array Filling' and tweak wording.

Author: ntrel

spec/arrays.dd

@@ -418,12 +418,12 @@ assert(s == [2, 3, 3, 4]);
 )
 
 
-$(H2 $(LNAME2 array-setting, Array Setting))
+$(H2 $(LNAME2 array-setting, Array Filling))
 
         $(P If a slice operator appears as the left-hand side of an assignment
         expression, and the type of the right-hand side is the same as the
-        element type of the left-hand side, then the array contents of the
-        left-hand side are set to the right-hand side.
+        element type of the left-hand side, then each element of the slice
+        expression will be assigned to the value on the right-hand side.
         )
 
 $(SPEC_RUNNABLE_EXAMPLE_RUN

spec/expression.dd

@@ -384,9 +384,13 @@ $(H3 $(LNAME2 simple_assignment_expressions, Simple Assignment Expression))
     as described in $(DDSUBLINK spec/arrays, resize, Setting Dynamic Array Length).
     )
 
-    $(LI If the lvalue is a static array or a slice, the behavior is as
+    $(LI If the left operand is a slice expression, the behavior is as
     described in $(DDSUBLINK spec/arrays, array-copying, Array Copying) and
-    $(DDSUBLINK spec/arrays, array-setting, Array Setting).
+    $(DDSUBLINK spec/arrays, array-setting, Array Filling).
+    )
+
+    $(LI If the lvalue is an array, the behavior is as described in
+    $(DDSUBLINK spec/arrays, assignment, Array Assignment).
     )
 
     $(LI If the lvalue is a user-defined property, the behavior is as