ZSH initialization file load sequence:

                        |
                  {/etc/zshenv}
                        |
                        |
                        | (is NO_RCS set?[1])
                        |
                        |
           [yes]        |     [no]
      ----------------------------------
      |                                |
      |                                |
      |                        {$ZDOTDIR/.zshenv}
      |                                |
      |                                | (is this a login shell?[2])
      |                                |
      |                         [yes]  |  [no]
      |                 -------------------------------
      |                 |                             |
      |          {/etc/zprofile}                      |
      |                 |                             | (is this shell
      |        {$ZDOTDIR/.zprofile}                   | interactive?[3])
      |                 |                             |
      |                 |                      [yes]  |  [no]
      |                 |                    -------------------
      |                 |                    |                 |
      |           {/etc/zshrc}         {/etc/zshrc}            |
      |                 |                    |                 | 
      |         {$ZDOTDIR/.zshrc}    {$ZDOTDIR/.zshrc}         |
      |                 |                    |                 |
      |                 |                    |                 |
      |           {/etc/zlogin}              |                 |         
      |                 |                    |                 |        
      |         {$ZDOTDIR/.zlogin}           |                 |
      |                 |                    |                 |
      |                 |                    |                 |
   **************************************************************** 
   *                             SHELL                            *
   **************************************************************** 
      |                 |                    |                 |
      |                 | (is NO_RCS         |                 |
      |                 | set?[1])           |                 |
      |                 |                    |                 |
      |          [yes]  |  [no]              |                 |
      |        -------------------           |                 |  
      |        |                 |           |                 |
      |        |         {$ZDOTDIR/.zlogout} |                 |
      |        |                 |           |                 |
      |        |           {/etc/zlogout}    |                 |
      |        |                 |           |                 |
      x        x                 x           x                 x

Tests are matched as follows, in increasing order of precedence;
`unsetopt OPTION' is equivalent to `setopt NO_OPTION' and `unsetopt
NO_OPTION' is equivalent to `setopt OPTION' in terms of precedence. 
For example, zsh -f with `unsetopt NO_RCS' in /etc/zshenv will source
/etc/zshenv, $ZDOTDIR/.zshenv, /etc/zshrc, and $ZDOTDIR/.zshrc.

[1]   DEFAULT                                   => [no]
      `setopt NO_RCS' called before test        => [yes]
      `-f' flag present on shell invocation     => [yes]
      `setopt RCS' called before test           => [no]
      
[2]   DEFAULT                                   => [no]
      first character of argument zero (name 
         by which zsh is invoked) is `-'        => [yes]
      `-l' flag present on shell invocation     => [yes]
      
[3]   DEFAULT                                   => [no] 
      `-i' flag present on shell invocation     => [yes]
      standard input is a tty and commands 
         are being read from standard input     => [yes]