Kristoffer Balintona has a nice post on Emacs occur. If you have moderate familiarity with Emacs, you have probably used occur on occasion. I use it all the time but still wasn’t aware of everything it could do.
Happily, Balintona is here to fill in the blanks. The information is all there in the documentation, of course, but it’s easy to miss it when skimming through the doc looking for the information that you need.
The first significant thing is that you can restrict the action of Occur to a specific region of the target buffer. You probably won’t want to do this very often but it’s easy to see how it could be useful. The second significant thing is the number of lines of context.
You can specify how many lines of context before and after the matching regex to include but you can also specify a string in which case what is displayed acts as a replacement string. You certainly won’t need that capability a lot but when you do, it’s perfect.
Take a look at Balintona’s post or the documentation for the details. This is another example of how learning Emacs is a lifelong endeavor. You learn bits and pieces of a certain functionality but later discover that it’s much richer than you believed.