What is the mechanism of the Diels-Alder reaction involving maleic anhydride as a dienophile?

In the Diels-Alder reaction with maleic anhydride as the dienophile, the diene (a molecule with two double bonds) reacts with the dienophile (a molecule with one double bond) to form a cyclic compound. The double bonds in the diene and dienophile break and new bonds are formed to create a six-membered ring structure. This reaction is a concerted process, meaning all bond-making and bond-breaking steps occur simultaneously.