Help module...or something like

Does someone know if it exists a module constructed to give help in specific modules/function/[phase or user variables or...]?
The idea is about a link (permanently on the top, or in a block, or somewhere) sensitive to the specific module/function call.
A possibility is a "doc", or a customized article type. 
But I've not found an "article display" function getting "title" or any textual input as parameter
for example
...?module=articles&ptid=9&title=nameoffunction
with "9"="helpdoc type".
and "nameoffunction"=$funcName

The standard response could be "None help found" in case of unexisting article; in case of existing one, the help can be displayed

Another idea is an hook function. Every http query can be added with an "&give=help" param, so the help text (it could be the summary, or a reducted help) can be displayed in the head/foot/block part of a module, explaining what the user can do.

Am I completely out, or there is something more simple, something already done, or someone has better ideas?

Please forgive my english...

Federico Luciani