Right now, it's impossible to generate valid XHTML by
using the nl2br() command, as it outputs a <br> tag.

It would be nice to change this to output a <br />
tag instead, which is fully backward compatible afaik,
and also valid XML (and hence XHTML).

Here's an extremely complicated patch that should hopefully accomplish this :-)

--- ext/standard/string.c.orig  Sat Dec 23 23:39:06 2000
+++ ext/standard/string.c       Sat Dec 23 23:40:48 2000
@@ -2304,7 +2304,7 @@ PHP_FUNCTION(nl2br)

        convert_to_string_ex(str);

-       php_char_to_str((*str)->value.str.val,(*str)->value.str.len,'\n',"<br>\n",5,return_value);
+       php_char_to_str((*str)->value.str.val,(*str)->value.str.len,'\n',"<br />\n",7,return_value);
 }
 /* }}} */