Where is the documentation for core associative arrays? I have been using Drupal for a few months now at work. I love the developer documentation, but I have to say, I feel like its incomplete -- either that, or I just don't know where to find the other half.

I see documentation for functions and hooks everywhere, but I don't see any documentation for the format of core data structures.

Example one: this page from the official docs has extensive explanation on hook_wysiwyg_editor_settings_alter, but it gives no complete disclosure what the $settings parameter can contain.

Example two: this page from the official docs has great explanation of the concept of "Render Arrays" and the functionality thereof, but has no description of the format of the associative array passed to the render() function, causing me to var_dump($user_page) for hours and come up with monstrosities like: &lt;?php echo $user_page["system_main"]["nodes"][$first_key]["field_objective"]["#object"]-&gt;field_targets["und"][0]["safe_value"]; ?&gt; on my custom .tpl.php files.

Is this information in the code itself, or somewhere else?
Render arrays are defined (in Drupal 7) with the hook_element_info hook.

To see what attributes a render element can accept you can check the MODULE_element_info function that defined it.

For example looking at system_element_info we can see that the page render element accepts a #show_messages attribute and that it contains a boolean value.

For more information you can also look for the template_preprocess_ELEMENT function for the element.

template_preprocess_page in our example.