The doctrine of equitable estoppel was not applicable where it did not appear that defendant did anything that he otherwise would not have done assuming that plaintiff had agreed to a reduction; the defendant had remedies available to which he did not avail himself, and plaintiff had not by her statements or conduct led defendant into his current situation. Lewis v. Lewis.
 Where, in a suit for child support arrearages brought by wife 16 years after decree of divorce was entered, wife’s claim was estopped, where from the evidence it could have been inferred that plaintiff did not expect child support from the defendant, but instead expected that such support would come form her second husband, and her conduct over the years was consistent with this position and there could have been little doubt but that she intended defendant to rely on such circumstances believing the necessity of modifying the decree of divorce unnecessary. Martin v. Comer.
 The doctrine of equitable estoppel can be applied as to all or part of past installments in an appropriate case. Johnson v. Johnson.
 The mere passage of time does not bring into effect the principle of equitable estoppel. Martin v. Comer.
 A mother was estopped from asserting any claim to support payment from her children’s father for the period of time that their daughter lived with him. Strum v. Strum.
 Nothing in subsection (a) of this section or this entire Act indicates that the legislature intended to abolish all actions in equity that existed for child support before the statute was enacted and the provisions of the Act did not preclude the court from entertaining a child custody and support action notwithstanding that the parties were divorced in England. Skilling v. Skilling.
 The trial court correctly relied on evidence outside the record when it noted that father noncustodial parent had some benefits available to him through his self-employment status as a farmer. In r Kern.