The "Predefined Variables" section of the manual needs some work, here are some thoughts:

(a) Document that register_globals affects environment variables. For example, if register_globals is turned off then to access DOCUMENT_ROOT one needs to do $HTTP_SERVER_VARS['DOCUMENT_ROOT'] as $DOCUMENT_ROOT will not work.  Also, use of getenv() is available, and now $_SERVER...
This is an important point.  Removing the $ in the description <term>'s seems appropriate too
(b) Link to security.registerglobals
(c) Link commandline to commandline docs
(d) Remove specific reference to php3/apache 1.3.6
(e) List new 4.1.0 variables, keep seperate from the others (for now)
(f) Mention of register_argc_argv near $argc & $argv
(g) Expand docs on difference between ENV and SERVER variables
(h) Add a See also: predefined constants and getenv()
(i) Briefly document the affect of variable scope
(j) Mention $GLOBALS
(k) Between SCRIPT_NAME, PATH_INFO, PHP_SELF and REQUEST_URI, which are available when (cgi vs. mod) and why windows users sometimes get php.exe
(l) Go through user notes, implement/delete as appropriate

Related doc bugs are #11833, #14093 and #14260