String.replace(/</g,'&lt;');

Three questions

1)

I have a string function that works perfectly but according to W3C.org
web site is syntactically flawed because it contains the characters </
in sequence. So how am I supposed to write this function?

String.replace(/</g,'&lt;');

2)

While I'm on the subject, anyone know why they implemented replace using
a slash delimiter instead of quotes? I know it's how it's done in Perl
but why is it done that way?

3)

One last regexp question:
is it possible to do something like this:
String.replace(/<(.*?)>(.*?)</$1>/ig,'&lt;$1&gt;$2&lt;/$1&gt;');
This is just an example where a sub-match used in a regular expression
must sub-match again exactly as it did the first time later in the same
string. But I don't know how to do that in a regexp although it seems
like it should be possible.