another newbie question -- auto-mode-alist regexp

[Robert P. J. Day]

  i've looked through both the emacs and elisp info pages, and
i haven't found a simple explanation for the syntax of the 
expression for setting the auto-mode-alist in my .emacs.

  a couple of examples that are part of the
(add-to-list 'auto-mode-alist ...  when i bring up online help
within emacs on the variable auto-mode-alist:

  ("\\.xml\\'" . xml-mode)
  ("\\.spec$" . rpm-spec-mode)
  ("\\.php[34]\\'\\|\\.php\\'\\|\\.phtml\\'" . php-mode)

what i haven't figured out yet:

1)  what means the sequence \\', as in what you see after
   ".xml" in that first example?  i can understand everything
   else, but that baffles me.

2) i assume that the "$" after .spec means end of string, which
  is familiar.  i'm curious why a lot of the other suffix regexp
  matches also don't match to end of string.  like the first one,
  .xml.  just curious.

3) regarding the php example, couldn't that have been written as
  
  ("\\.php[34]?\\'\\|\\.phtml\\'" . php-mode)


(this assumes that i still don't know what \\' means.)

  a pointer to the correct online help or info page would do
nicely.  thanks for your patience.

rday