``Simple vectors'' in Guile 1.7

[Ludovic Courtès]

Hi,

The manual of Guile 1.7 reads:

  A vector can be read and modified from C with the functions
  `scm_c_vector_ref' and `scm_c_vector_set_x', for example.  In addition
  to these functions, there are two more ways to access vectors from C
  that might be more efficient in certain situations: you can restrict
  yourself to "simple vectors" and then use the very fast _simple vector
  macros_

However, it fails to describe what a ``simple vector'' is and when the
user can safely use these macros.  Any hint?

Thanks,
Ludovic.