Right now, the search/find in the code tab only works within one tab. If there are .nls files, you have to open them first before you can search. This makes it very laborious to find where things are (e.g., everyone a global is used across all files). It would be great to be able to search and see matches across all .nls files in the project.
I fully agree. Whenever I need to read and understand somebodies program that is split up in .nls files, I copy them all back into the main file. Without being able to search across all files involved, and/or to use the very convenient feature that allows you to jump to the declaration of a variable, and whereever it has been used, should work across all files. - I have no idea, though, how much work it would be to implement this feature.
I agree that all included files should be searchable regardless of whether they are open or not. This could go along with the following open issue on GitHub: Unified Find dialog · Issue #2466 · NetLogo/NetLogo · GitHub.