In many cases, the existing source code includes tab, and new-line may be different from the platform default.
It's helpful if we have an option to set those characters visible in the Editor.

  * tab
  * white space
  * new-line (CR, CR+LF, LF)
  * ideographic space (unicode u3000)

When editing in the east Asian locale, ideographic space (u3000) is accidentally inserted (it's expected to insert white
space). It's really helpful if ideographic space can be displayed in the editor.

Here is a screen shot image. It's an Eclipse plugin which Japanese developer is providing similar feature:
http://eclipsewiki.net/eclipse/index.php?plugin=ref&page=JStyle%A5%D7%A5%E9%A5%B0%A5%A4%A5%F3&src=jstyle.png