Tabs "can be displayed completely differently on different types of systems and editors"?

Question

While reading the arguments against using tabs, I came across this ( source ):

... it might be a good idea to avoid tabs alltogether, because the semantics of tabs are not very well defined in the computer world, and they can be displayed very differently for different types of systems and editors .

I am relatively new to programming and have never experienced tabbed issues in my code, and I have used a number of editors, including Notepad ++, Programmer Nodepad, Gedit, Kate, Sublime Text, etc. Perhaps I haven’t done enough coding to get to this point, so the question is:

Can someone explain, simply in words, what the quote means? And is the tab issue still relevant?

---

Please note that I am not asking you if I should use tabs or spaces in my code. I only after a rational explanation of the specific argument against the tabs that I met.

Answer 1

I assume that you want to see some examples, so I have listed some of the most common.

Problem number 1: tab width is not consistent

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Answer 2

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