If a person claiming an interest desires to raise any question concerning the validity of a tax title, the person shall do so by answer filed in the proceeding on or before the return day, or within that further time as may on motion be allowed by the court, providing the motion is made prior to the fixed return date, or else be forever barred from contesting or raising the question in any other proceeding. He or she shall also file specifications setting forth the matters upon which he or she relies to defeat the title; and unless the specifications are filed, all questions of the validity or invalidity of the title, whether in the form of the deed or proceedings relating to the sale, shall be deemed to have been waived. Upon the filing of the specifications, the court shall hear the parties and shall enter a decree in conformity with the law on the facts found.