Often when reading scientific literature, one has to quickly jump between certain pages (eg text and appendix or literature). A great way to improve the workflow in this condition would be the option to quickly jump between marks, for example by including little arrows left and right of the mark button. One could mark the appendix site and afterwards, when reading through the text, mark the current side, jump with the right arrow to the appendix, and then jump back to the current side using the left arrow.