[manual] fftw unclear to me

[Francesco Potorti`]

In the manual, I read:

     Manage FFTW wisdom data. Wisdom data can be used to significantly
     accelerate the calculation of the FFTs but implies an initial cost
     in its calculation. The wisdom used by Octave can be imported
     directly, usually from a file /etc/fftw/wisdom, 

What does this mean?  Precisely, what "directly" means?  What "usually"
means?  Does Octave read /etc/fftw/wisdom at startup?  If not, how can
one read it?

          WISDOM = fftw ('dwisdom')

     will save the existing wisdom used by Octave to the string WISDOM.
     This string can then be saved in the usual manner. 

What is "the usual manner"?  If it means using 'save', that should be
specified.

     However, the wisdom data can be reloaded if it is saved to a file
     as described above.  

Same as above: if this means using 'load', that should be specified.

			  Also, any system-wide wisdom file that has
     been found will also be used.

Does this answer my question above?  I mean, does this mean that Octave
reads /etc/fftw/wisdom at startup?