Document array literals

lib/Language/syntax.pod

@@ -328,11 +328,26 @@ Long forms with explicit values:
     :thing['some', 'values']    # same as  thing => ['some', 'values']
     :thing{a => 'b'}            # same as  thing => { a => 'b' }
 
-=begin comment
-
 =head3 Array literals
 
-TODO
+A pair of square brackets can surround an expression to for an
+itmized L<Array|/type/Array> literal; typically there is a comma-delimited list
+inside:
+
+    say ['a', 'b', 42].join(' ');   # a b 42
+    #   ^^^^^^^^^^^^^^ Array constructor
+
+The array constructor flattens non-itemized arrays and lists, but not itemized
+arrays themselves:
+
+    my @a = 1, 2;
+    # flattens:
+    say [@a, 3, 4].elems;       # 4
+
+    # does not flatten:
+    say [[@a], [3, 4]].elems;   # 2
+
+=begin comment
 
 =head3 Hash literals