DOCBOOK: Displaying <legalnotice> when it is in a <artheader>?

[Stephane Bortzmeyer <bortzmeyer@pasteur.fr>]

Apparently, the Modular Stylesheets do not display the <legalnotice> 
when it is in the <artheader> of an <article> (in TeX and HTML output).

Specific question: what could I put in my custom stylesheet to display 
it? It does not seem documented.

General question: it is common for some elements to be hidden in some 
contexts (like the <citetitle> in a <biblioentry>, see my message on 
"Web servers in <bibliography>?"). Is there a general way to display 
them?

(element (artheader legalinfo) (do-something)) 

seems ignored.