Change signup template

Trying to edit the signup page.

I followed the guide here: http://www.amember.com/docs/Themes_and_Templates.

Can anyone explain this code block in "application/default/themes/mytheme/signup/signup.phtml"

Code:

<div class="am-signup">
<?php echo $this->blocks('signup/login/before') ?>
<?php include $this->_script('signup/_login.phtml'); ?>
<?php echo $this->blocks('signup/login/after') ?>

<?php echo $this->blocks('signup/form/before') ?>
<?php include $this->_script('_form.phtml'); ?>
<?php echo $this->blocks('signup/form/after') ?>

</div>

What do these lines mean

Code:

<?php echo $this->blocks('signup/login/before') ?>

can I hook into blocks somehow?

Is the only way to change the signup form using the form editor in amember4 backend?

I found this thread which answered many of my questions. Since it is more relevant my post can be closed. Thanks.