Added docs for Baggy.grabpairs

doc/Type/Baggy.pod

@@ -39,7 +39,30 @@ probabilities stay consistent through subsequent C<grab> operations.
 
 =head2 method grabpairs
 
-=comment TODO
+Defined as:
+
+    multi method grabpairs(Baggy:D:) returns Any
+    multi method grabpairs(Baggy:D: $count) returns List:D
+
+Returns a C<Pair> or a C<List> of C<Pair>s depending on the version of the method
+being invoked. Each C<Pair> returned has an element of the invocant as its key and the
+elements weight as its value. Unlike L<pickpairs>, it works only on mutable structures,
+e.g. L<BagHash|/type/BagHash>. Use of C<grabpairs> on 'an immutable structure results in
+an C<X::Immutable> exception. If C<*> is passed as C<$count>, or C<$count> is greater
+than or equal to the number of L<elements|#method elems> of the invocant, then all
+element/weight C<Pair>s from the invocant are returned in a random sequence.
+
+What makes C<grabpairs> different from L<pickpairs|#method pickpairs> is that the
+'grabbed' elements are in fact removed from the invocant.
+
+    my $breakfast = (eggs => 2, bacon => 3).BagHash;
+    say $breakfast.grabpairs;                         # bacon => 3
+    say $breakfast;                                   # BagHash.new(eggs(2))
+    say $breakfast.grabpairs(1);                      # (eggs => 2)
+    say $breakfast.grabpairs(*);                      # []
+
+    my $diet = ('eggs' => 2, 'bacon' => 3).Bag;
+    say $diet.grabpairs;                              # throws X::Immutable exception
 
 =head2 method pick