Can somebody clue me in on what this does, or point me to documentation of it?

Thanks

$xoopsOption is an array of options used by XOOPS in some aspects to show the page correctly.

E.g.
$xoopsOption['template_main'] sets the template to be used in the main contents (module output area)

$xoopsOption['theme_use_smarty'] is a setting to determine whether the theme uses smarty or not.

$xoopsOption['pagetype'] can be either admin or user and determines which language files are included, admin or user.

$xoopsOption['nocommon'] if set to 1 will not include common.php

There are a few more to disable certain blocks, if you should desire that, but I have rarely found a reason to do so. The most used is $xoopsOption['template_main'].

Thank you again Mithrandir