Oh.. I've built for myself a short list of things doable with `tikzmark`, so it may help you.
1): highlighting -> http://tex.stackexchange.com/questions/51582/background-coloring-with-overlay-specification-in-algorithm2e-beamer-package
2): highlighting and add comments -> http://tex.stackexchange.com/questions/57060/mark-a-pseudocode-block-and-insert-comments-near-it
3): mark digits -> http://tex.stackexchange.com/questions/76060/combine-two-tikzmark-solutions
4): mark positions, insertion of labels in arrrows -> http://tex.stackexchange.com/questions/76506/label-steps-of-equations-usin…