[Zope] what is error_message and how do I alter it??

[Trevor Toenjes]

I am trying to improve the usability of the standard_error_message for a
public site. like adding a search, suggestions for what users might be
looking for, etc.
However this part of the standard_error_message has stumped me.

<dtml-if error_message>
  <dtml-var error_message>
<dtml-else>

I have read the one how-to I could find and some threads, but no real
solutions.
What is error_message?
Where does the autoformatting come from, and how do I alter it?
Can I modify it to just grab the error and not all the other Zope stuff?

Is there a library of these error messages that can be modified to provide
better information for users to find what they are looking for.  they come
from somewhere?
Formulator allows you to customize your error messages. Shouldn't this be as
open?

Why is this so stealthy compared to the rest of Zope?
Why should I have to turn off debugging for tracebacks to be commented out
in the HTML?
If it is an object, then I can include it or not in my
standard_error_message, right.
So if I have error_tb in my standard_error_message, then it renders, if
not - it's hidden.
Why isn't it treated like an object like the rest of Zope?

I cannot find any products that handle error_messages or address user
usability.

Sorry for the rant.  I am new to Zope.  ;)
Am I missing something?

Thanks for the help,
Trevor