+val set_offset_int : 'a field -> int -> 'a field
+(** Set the offset expression for a field to the given number.
+
+ The effect is that the field [{ _ : 8 : offset(160) }] could
+ be created by calling [set_offset_int field 160]. *)
+
+val set_offset : 'a field -> expr -> 'a field
+(** Set the offset expression for a field to the given expression.
+
+ The effect is that the field [{ _ : 8 : offset(160) }] could
+ be created by calling [set_offset_int field <:expr< 160 >>]. *)
+
+val set_no_offset : 'a field -> 'a field
+(** Remove the offset expression from a field. The field will
+ follow the previous field, or if it is the first field will
+ be at offset zero. *)
+