how do I use super-sed's /S option?

 I'm trying to use super-sed's perl regex /S  flag, but can't get it to work at all. This would be a very handy tool, if only I could understand how it's used! For example, I expect the following command will match and replace the pattern which spans across a newline to be replaced with Xs: 
 echo "(123) 456-7890\n(456) 567-9050" | sed -R -e "s/78.*?5/x/S" So, I am expecting this output: 
 (123) 456-78XX XXXXXXX67-9050 Instead I get (no match): 
 (123) 456-7890 (212) 567-9050 


 





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