Are there any invisible characters? I have checked Google for invisible characters and ended up with many answers but I'm not sure about those. Can someone on Stack Overflow tell me more about this?
Also I have checked a profile on Facebook and found that the user didn't have any name to his profile? How can this be possible? Is it some database issue? Hacking or something?
When I searched over Internet, I found that 200D is an ASCII value with an invisible character. Is it true?
An invisible Character is ?, or U+200b
?
I just went through the character map to get these. They are all in Calibri.
Number Name HTML Code Appearance ------ -------------------- --------- ---------- U+2000 En Quad   " " U+2001 Em Quad   " " U+2002 En Space   " " U+2003 Em Space   " " U+2004 Three-Per-Em Space   " " U+2005 Four-Per-Em Space   " " U+2006 Six-Per-Em Space   " " U+2007 Figure Space   " " U+2008 Punctuation Space   " " U+2009 Thin Space   " " U+200A Hair Space   " " U+200B Zero-Width Space ​ "" U+200C Zero Width Non-Joiner ‌ "" U+200D Zero Width Joiner ‍ "" U+200E Left-To-Right Mark ‎ "" U+200F Right-To-Left Mark ‏ "" U+202F Narrow No-Break Space   " "
Other answers are correct -- whether a character is invisible or not depends on what font you use. This seems to be a pretty good list to me of characters that are truly invisible (not even space). It contains some chars that the other lists are missing.
'\u2060', // Word Joiner
'\u2061', // FUNCTION APPLICATION
'\u2062', // INVISIBLE TIMES
'\u2063', // INVISIBLE SEPARATOR
'\u2064', // INVISIBLE PLUS
'\u2066', // LEFT - TO - RIGHT ISOLATE
'\u2067', // RIGHT - TO - LEFT ISOLATE
'\u2068', // FIRST STRONG ISOLATE
'\u2069', // POP DIRECTIONAL ISOLATE
'\u206A', // INHIBIT SYMMETRIC SWAPPING
'\u206B', // ACTIVATE SYMMETRIC SWAPPING
'\u206C', // INHIBIT ARABIC FORM SHAPING
'\u206D', // ACTIVATE ARABIC FORM SHAPING
'\u206E', // NATIONAL DIGIT SHAPES
'\u206F', // NOMINAL DIGIT SHAPES
'\u200B', // Zero-Width Space
'\u200C', // Zero Width Non-Joiner
'\u200D', // Zero Width Joiner
'\u200E', // Left-To-Right Mark
'\u200F', // Right-To-Left Mark
'\u061C', // Arabic Letter Mark
'\uFEFF', // Byte Order Mark
'\u180E', // Mongolian Vowel Separator
'\u00AD' // soft-hyphen
There is actually a truly invisible character: U+FEFF.
This character is called the Byte Order Mark and is related to the Unicode 8 system. It is a really confusing concept that can be explained HERE The Byte Order Mark or BOM for short is an invisible character that doesn't take up any space. You can copy the character bellow between the > and <.
Here is the character:
> <
How to catch this character in action:
> and <,You will notice that when your caret gets to the place you pasted the character, it will briefly stop for around half a second. This is becuase the caret is passing over the invisible character. Even though you can't see it doesn't mean it isn't there. The caret still sees that there is a character in that area that you pasted the BOM and will pass through it. Since the BOM is invisble, the caret will look like it has paused for a brief moment. You can past the BOM multiple times in an area and redo the steps above to really show the affect. Good luck!
EDIT: Sadly, Stackoverflow doesn't like the character. Here is an example from w3.org: https://www.w3.org/International/questions/examples/phpbomtest.php
Source: Stackoverflow.com