+ * Returns the value of field 'viewId'. The field 'viewId' has
+ * the following description: additional identifier which
+ * properly disambiguates
+ * the structure view from any other view with the same
+ * attributes. This is not an ID,
+ * because it is possible to have many references to the same
+ * physical structure view
+ * from different sequences in an alignment. A structureState
+ * element citing the same
+ * viewId will appear for each instance.