How to I insert ALT CODES?

Question

I want to insert ALT codes into a document on Linux.

Like ones from https://area51.stackexchange.com/

How to achieve this?

Answer 1

To make ALT CODES,

Type in what you want (e.g. u2222 = ∢) While holding down CTRL and SHIFT.

Then once you have written the Alt code release the two keys.

(When you are typing it it should be Underlined.