According to the documentation:

  :help [I

> Display all lines that contain the keyword under the cursor. Filenames and line numbers are displayed for the found lines. The search starts at the beginning of the file.

  :help [_CTRL-I

> Jump to the first line that contains the keyword under the cursor.

Both "] I" and "] CTRL-I" will start at the current cursor position instead.

I did not know about these, but now I am wondering how to reverse "] CTRL-I" and go to the previous result, as it seems quite useful.

The key is that it recursively searches (for instance in C++) header files for the word under the cursor and brings you to the first result. To go backward 'CTRL-O' jumps back in the jump list. I've not yet found a way to go to the next item in the '] CTRL-I' list. so I 'CTRL-O' then '2 [ CTRL-I', etc.