+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * This class manages the collection of hidden columns associated with an
+ * alignment. To iterate over the collection, or over visible columns/regions,
+ * use an iterator obtained from one of:
+ *
+ * - getBoundedIterator: iterates over the hidden regions, within some bounds,
+ * returning *absolute* positions
+ *
+ * - getBoundedStartIterator: iterates over the start positions of hidden
+ * regions, within some bounds, returning *visible* positions
+ *
+ * - getVisContigsIterator: iterates over visible regions in a range, returning
+ * *absolute* positions
+ *
+ * - getVisibleColsIterator: iterates over the visible *columns*
+ *
+ * For performance reasons, provide bounds where possible. Note that column
+ * numbering begins at 0 throughout this class.
+ *
+ * @author kmourao
+ */
+
+/* Implementation notes:
+ *
+ * Methods which change the hiddenColumns collection should use a writeLock to
+ * prevent other threads accessing the hiddenColumns collection while changes
+ * are being made. They should also reset the hidden columns cursor, and either
+ * update the hidden columns count, or set it to 0 (so that it will later be
+ * updated when needed).
+ *
+ *
+ * Methods which only need read access to the hidden columns collection should
+ * use a readLock to prevent other threads changing the hidden columns
+ * collection while it is in use.
+ */