Invisible characters - ASCII

问题

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?

回答1:

How a character is represented is up to the renderer, but the server may also strip out certain characters before sending the document.

You can also have untitled YouTube videos like https://www.youtube.com/watch?v=dmBvw8uPbrA by using the Unicode character ZERO WIDTH NON-JOINER (U+200C), or ‌ in HTML. The code block below should contain that character:

‌‌ 

回答2:

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         " "

来源：https://stackoverflow.com/questions/17978720/invisible-characters-ascii