Reference for special character input with dead keys

On Linux/Ubuntu, I have found a few options for entering special characters:

• AltGr+Key and Shift+AltGr+Key on keyboards that have AltGr; those can be found on the Keyboard Layout Chart in Ubuntu. For example, Shift+AltGr+Q produces Ω.
• Unicode input with Shift+Ctrl+U <unicode> <RET>, which works in almost all applications in Ubuntu 17.04 and in GTK applications for older Ubuntu versions and other distributions. For example, Shift+Ctrl+U 2209 <RET> creates ∉
• The Compose key which, after enabling, combines two characters to one, for example <Compose> 1 2 produces ½ or <Compose> B . produces Ḃ.
• And finally, dead keys like ~ and ^ which do not immediately produce a character but modify the keyboard layout for the next key press. For example, ~ a produces ã, ~ = produces ≃, ^ i produces î, and ^ ^ produces ^.

Where can I find a reference for dead keys?