(e) The duty to provide support for a minor child shall continue
until the child reaches the age of majority, dies, marries, or
becomes emancipated, whichever first occurs; provided, however,
that, in any temporary or final order for child support with respect
to any proceeding for divorce, separate maintenance, legitimacy, or
paternity entered on or after July 1, 1992, the trier of fact, in
the exercise of sound discretion, may direct either or both parents
to provide financial assistance to a child who has not previously
married or become emancipated, who is enrolled in and attending a
secondary school, and who has attained the age of majority before
completing his or her secondary school education, provided that such
financial assistance shall not be required after a child attains 20
years of age. The provisions for support provided in this
subsection may be enforced by either parent or the child for whose
benefit the support is ordered.
(f) The provisions of subsection (e) of this Code section shall be
applicable only to a temporary order or final decree for divorce,
separate maintenance, legitimation, or paternity entered on or after
July 1, 1992, and the same shall be applicable to an action for
modification of a decree entered in such an action entered on or
after July 1, 1992, only upon a showing of a significant change of
material circumstances.
So, what does subsection (f) mean if the modification is filed after 7-1-92? How is significant change of material circumstances "proved?"