We can also create bookmarks that are assigned to a digit (0 to 9) or letter (A to Z). To add a mnemonic line bookmark, press F3 (macOS) / F11 (Windows/Linux) and press the digit or letter to use as an identifier for this bookmark. Again, we can also or right-click the gutter next to the line of code that you want to bookmark and select Add Mnemonic Bookmark.

Optionally, we can provide a description for the new bookmark. We can double-click the digit or letter we want to assign.

Lines marked with mnemonic bookmarks have the corresponding digit or letter icon in a frame.

If the selected digit or letter is already in use, IntelliJ IDEA will ask you whether you want to overwrite an existing bookmark with the new one. When we select the Don't ask again option, the IDE will silently overwrite mnemonics.