I was reviewing a NuttX RTOS PR (Pull Request) and facing a challenge: I want to suggest to change a text in a line from a Kconfig file that starts with two TABs characters, but pressing the keyboard tab key just move to the next page component.

Searching for a solution I discovered that GTK+ on Linux supports a feature similar to Windows to enter special characters. On Windows if you press ALT and type 09 it will enter the TAB character (in fact you can use it to type any character, you can even create simple executables).

On Linux you need to enter this more complex sequence (otherwise it is not Linux) here:
Ctrl + Shift + u
type 9 and press Enter or Space

Source: https://superuser.com/questions/67934/typing-the-tab-character-in-browser-text-boxes