What does the law mean by best interests of the child?

Section 5338 of the Child Custody Act, 23 Pa.C.S. § 5321 et seq., implements changes to requests to modify existing custody orders. That section provides that, upon petition, a trial court may modify a custody order if it serves the best interests of the child. Section 5328(a), in turn, sets forth a list of 16 factors. When a party files a petition for modification of a custody order, the trial court must perform an analysis of the best interests of the child giving consideration to all 16 of the factors set forth in section 5328(a). E.D. v. M.P., 33 A.3d 73 (Pa.Super. 2011).