m    Treat string as multiple lines.  
     That is, change "^" and
     "$" from matching the start or end of the string to
     matching the start or end of any line anywhere within
     the string.

s    Treat string as single line.  That is, change "." to
     match any character whatsoever, even a newline, which
     normally it would not match.
[download]

I had problems with perldoc too, when I started to learn perl.
For a beginner the best she/he can do is buy the camel book.

But for a quick lookup of syntax the best is perldoc!

This text is also present in the 5.005_03 documentation.

Even the documentation that came with perl5.004 includes those two paragraphs:

    m     Treat string as multiple lines.  That is, change "^"
          and "$" from matching at only the very start or end of
          the string to the start or end of any line anywhere
          within the string,

    s     Treat string as single line.  That is, change "." to
          match any character whatsoever, even a newline, which
          it normally would not match.
[download]

Although it lacks the followup explanation of the interactions between /s, /m, and $*.

The original poster must have a very old version of Perl. Complaining about a lack of documentation in such an old version of Perl is pointless. The problem was found and fixed years ago; the solution is to upgrade.

I must say that I rarely use perldoc for the core, except for the always useful perldoc -f func.

Instead I rely on books, especially the Camel 3.

I often use perldoc with modules though. As soon as you install a new module it's doc is accessible using perldoc module. That's very cool!

andy.

P.S.: /s is matching \n with ., /m is handling ^ and $ after and before each \n :-)
--
Alfie