Note: I have frequently seen the use of sed's s parameter use slashes. The "sed" command is commonly found in Unix, and is downloadable for Windows. Here is an example:
echo I like blue apples | sed s/blue/red/
(That command will say "I like red apples". The part between the first couple of slashes gets replaced by the part between the next couple of slashes.)
Actually, I could also have said "sed s!blue!red!" because sed doesn't care much about which character is used as a separator, as long as each separator matches the first one used (right after the letter "s" in the parameter). That said, I have seen slashes used as the separator very, very frequently.
Especially when I suspect I am among a Unix-literate group, I might often point out speling errors (as shown in the example).
I know this doesn't precisely match the example you gave, but it is usage that I've seen frequently, so I figured it can be worth being aware of (especially if you did encounter a case of s/old/new/ but just didn't remember the s at the start.