How should I interpret the fact that a Unicode code point is shown in two completely different ways in two different terminal emulators?

Question

This is kind of a spin off from an older question I asked.

Here's the screenshot from that question:

• In the bottom left is URxvt, and you can see a lighting bolt-like icon at the beginning of the prompt, that's "\ue00a";
• in the bottom right is xfce-terminal from Xfce, and you can see that it renders the very same "\ue00a" Unicode point in a very different way!

I was under the impression that when I read something like "\ue00a", "\u263b", "\u1d43d" and so on, I'm most likely looking at the identity of a symbol, as defined by Unicode.

However, how strange would the definition need to for it to allow 2 terminal emulators to show it so differently?

Incidentally, I don't know how much of this is due to the terminals and how much to the fonts.

I am asking this question (like the other I linked) in order to get a better understanding of the whole matter.

Answer 1

U+E000 to U+F8FF is a private-use area. It's reserved to allow systems to store and display characters that are not present in Unicode. So you can't expect it to have a consistent appearance (or indeed to appear as anything other than a blank space or replacement character).

If you want a lighting-like character in Unicode, you can try drawing it on Shapecatcher (but it doesn't know all of Unicode, especially not Emoji), or search through Unicode character names. I can't find a lightning bolt character exactly like the one in your screenshot, but there's U+26A1 HIGH VOLTAGE SIGN (⚡) and U+1F5F2 LIGHTNING MOOD (🗲) which are visually close. There are meteorological symbols U+2607 LIGHTNING (☇), U+2608 THUNDERSTORM (☈) and U+26C8 THUNDER CLOUD AND RAIN (⛈) which are semantically related but visually very different.