[Zope] this().aq_explicit() & this().document_src() - what is the relationship?

[Fabio Rolando]

Hi,
I have a ZClass with DTMLDocument as base class. I made a DTMLMethod to 
display the contents of the Object with

<dtml-var "this()">

but I got the HTML tag escaped (i.e. < transformed in &lt; and so on)

so I changed in

<dtml-var "this().document_src()">

and it worked correctly, with the HTML rendered, but I got problems with 
unauthenticated user, getting the message

Error.... document_src not allowed in this context.

So I changed (practically by mistake!) to

<dtml-var "this().aq_explicit()">

It works correctly with no authentication problem! Now I am happy, yet a 
bit frustrated because I could not find any document around helping me 
understanding the reason WHY it does work now!  :-| I don't even understand 
what is the relationship between aq_explicit() and the contents of the 
document.

Any pointer, suggestion, hint, whatever...?

Thank you so much
Fabio