It would be great to make search and replace limit itself to the active selection if it is present. Sometimes I need to replace an index `j` in a formula to an index `k` but if I start a math replace the program starts replacing in the full document, even if I highlight only the formula I am interested in. Furthermore, if the same document is opened in two different windows the search and replace mechanism starts acting on a random window, rather than the one that was active when search and replace was called.

Respecting the highlighted area is the default behavior in gui editors and in editors like emacs (search and replace by default restricts to the "region" if it is active)