Using TextMate on Mac, the "invisibles" can be displayed by using
View -> Show Invisibles
But the space vs tab characters are not shown, and Preferences doesn't seem to have any entry to change that either. Is there a way to show them? It is because some older coder may have tab or space mixed together so what looks good in the editor may actually be misaligned. (editor shows tab as 2 spaces)
Tab characters are shown, but spaces are not. What's probably happening is that you have Soft tabs turned on, in which case the tabs are converted into spaces automatically.
alt text http://grab.by/grabs/fabaea391dc8bc764636f0ca19a8c38d.png
In this picture there is a tab character, new line, tab character, new line, soft tab, new line
See this thread for an explanation as to why spaces are not shown.
Here is where you can change soft/real tabs. alt text http://grab.by/grabs/783db3a88609a01c7702cbd250f495c6.png