Last week we’ve discussed various kinds of comments in IDA’s disassembly and pseudocode views.
In fact, the comments are also available for Structures and Enums. You can add them both for the struct/enum as a whole and for individual members. Similar to the disassembly, regular and repeatable comments are supported.
Repeatable comments are duplicated in the listing when the enum or structure member is used.
One interesting use of this is for C++ class vtables (or any struct with pointers): if you add the comment with the method’s address in the vtable structure, it will be printed in disassembly and you can double-click it to jump to the implementation or hover over it to see a hint window with disassembly.