Search for <old> and replace it with <new> in <range> (defaulting to the current line). The character following the command is used as a seperator (a space in the example). This allows for the sed-like syntax: s/old/new/. The command 'sed' will use strsed() with regular expressions, the command 'sub' or 's' will use strsub() with literal matching. Options are any one of:
g Globally match and replace (do it multiple times)
s Single match and replace (do it only on the first occurance)
c Case matters when matching.
i Case doesn't matter when matching.
Option defaults for sed are: si
Option defaults for sub are: gi