1. A computer implemented method comprising: accessing markup language data comprising markup language elements; processing the markup language data, with a headless browser without display in a graphical user interface, to generate a document object model (“DOM”) tree; based at least in part on the DOM tree, generating a single-hierarchical DOM data structure describing at least two elements in the markup language data, wherein the elements are representative of presentation of the markup language elements; accessing two or more layout rules comprising a first layout rule and a second layout rule, wherein the first layout rule comprises a tolerance specifying that two or more elements overlaying one another during presentation constitutes a layout error, wherein the tolerance is represented by a first amount of pixels, wherein the second layout rule comprises a number of layers permitted to an element based at least in part on a rendering capability of a device; determining a first application of the first layout rule to the DOM data structure; determining a second application of the second layout rule to the DOM data structure; determining that a layout error is not present in the second application; determining that a layout error is present in the first application, wherein the layout error is represented by a first amount of pixels; determining a second amount of pixels by which the layout error exceeds the tolerance; generating verification results based at least in part on the second amount of pixels; and generating, using the second amount of pixels, one or more corrective relocation recommendations including a third amount of pixels by which to displace at least one of the at least two elements.