Doc: clarify role of functions.  Abramo Bagnara.
Doc: clarify role of functions.  Abramo Bagnara.

edechter/swipl-devel,edechter/swipl-devel,jn7163/swipl-devel,koryonik/swipl-devel,mndrix/swipl-devel,mndrix/swipl-devel,koryonik/swipl-devel,mndrix/swipl-devel,koryonik/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel,jn7163/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,jn7163/swipl-devel,jn7163/swipl-devel