Description
Providing a distinct symbol for each invisible character (BOM, Combining Grapheme Joiner, Left-to-right mark / Right-to-left mark, Soft hyphen Word joiner, Zero-width joiner, Zero-width non-joiner, Zero-width space) is really useful while creating UI and processing text. (https://en.wikipedia.org/wiki/Universal_Character_Set_characters#Special-purpose_characters)
https://www.microsoft.com/typography/otfntdev/glyphs.htm
https://commons.wikimedia.org/wiki/Category:IEC_60417_symbols
When you are coding you want to see such characters. They are needed to be invisible only for the end-users. Similar to clicking on ¶ when you are authoring a document in MS word or other text-editors.
For example, copy and run this in js console: "OK"=="OK"
. It returns false. Do you know why?
The advantages of being able to see theses invisible characters are specially clear for me and whose their writing system use such characters frequently (Persian, German, Hebrew, …).
There are not many invisible special purpose characters. these should be enough to be included: