question about note on php.net

Hello, I have a question--is the note from equazcion here correct? It is left unchallenged on the page but I can't see how it is correct since I am under the impression that the environment is refreshed each page load and the function or method definitions (including those for session_set_save_handler) would need to be re-established each page, not each session. I am having tremendous difficulty debugging some code I wrote and eliminating my uncertainty regarding this point would be greatly helpful. Any advice would be appreciated. Thanks!