A uv variable can change its value in any part of the
uv variable stream. So it can change its value after each call to
uvread, uvnext or uvscan. The uv routines which need to
know if a uv variable has changed (uvprobvr, uvcopyvr and
uvupdated) normally (i.e. by default) work on whether the particular
variable(s) of interest has changed since the last ``mark'' in the uv stream.
By default any routine which
causes more of the uv stream to be read (uvread, uvscan and
uvnext) move this marker to the current point in the uv stream, before
reading more. The uvmark routine provides greater control at
marking the position in the stream. Calling
When Do UV Variables Change?
sets the marker at the current position in the uv file, and disables
uvread, etc, from resetting the marker. Calling
also sets the marker at the current position, and enables uvread, etc,
to reset the marker on each call.