[link|http://www.cornerstonemag.com/sed/|http://www.cornerstonemag.com/sed/]

And I believe you're right:
s/regular expression/replacement/flags
Substitute the replacement string for instances of the regular expression in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the RE and the replacement. Within the RE and the replacement, the RE delimiter itself can be used as a literal character if it is preceded by a backslash. An ampersand (&) appearing in the replacement will be replaced by the string matching the RE. The special meaning of "&" in this context can be suppressed by preceding it by backslash. The characters \\n, where n is a digit, will be replaced by the text matched by the corresponding backreference expression. For each backslash (\\) encountered in scanning replacement from beginning to end, the following character loses its special meaning (if any). It is unspecified what special meaning is given to any character other than &, \\ or digits. A line can be split by substituting a newline character into it. The application must escape the newline character in the replacement by preceding it by backslash. A substitution is considered to have been performed even if the replacement string is identical to the string that it replaces. The value of flags must be zero or more of:

n
Substitute for the nth occurrence only of the regular expression found within the pattern space.
g
Globally substitute for all non-overlapping instances of the regular expression rather than just the first one. If both g and n are specified, the results are unspecified.
p
Write the pattern space to standard output if a replacement was made.
w wfile
Write. Append the pattern space to wfile if a replacement was made.