If you ***add two spaces*** after a word and enter a line break/return, the markdown engine will insert a line break automagically. This disables the rewrapping that is designed into the editing system.

So
if 
you
enter
lines
like
this, they wrap.

But   
if  
you  
double  
space, then they don't wrap.

(click the edit link to see my source)

This is documented in the [advanced editing help][1] section, which you can get to from any editing frame by clicking the blue circle around the question mark to the right of the edit toolbar.


  [1]: http://apple.stackexchange.com/editing-help