  A virtual string can be defined as an equivalence class of planar diagrams
under certain kinds of diagrammatic moves. Virtual strings are related to
virtual knots in that a simple operation on a virtual knot diagram produces a
diagram for a virtual string.
  In this paper we consider three operations on a virtual string or virtual
strings which produce another virtual string, namely covering, composition and
cabling. In particular we study virtual strings unchanged by the covering
operation. We also show how the based matrix of a composite virtual string is
related to the based matrices of its components, correcting a result by Turaev.
Finally we investigate what happens under cabling to some invariants defined by
Turaev.
