While exploring lots of tricks to store and retrieve data/metadata into the
simpler way, I found thar this html structure:
<span class="metadata" title="name">content</span>
where css states that
.metadata {display:none;}
is an excellent, invisible data container, accessible both to a js into a
local page and by a bot parsing html of the page from an ?action=render
call. Such a html tag can be produced by a very simple template with two
parameters, and calling such a template could be done with something like
{{Metadata|name|content}}
so allowing metadata retrieval from wiki code too.
I think that such a simple structure extremely promising.
Alex