usage helpers



Hello,
 Is there a routine analogous to the ? or ?? for user defined routines. 
 Up to now, I have been making my own. For instance, I have a routine 
which generates the Jacobian matrix of a function f from R^m to R^n.

I use
 Jmat_usg: print(" "Jmat(f,x) gives the Jacobian matrix of the function 
f:R^m -> R^n");

The problem with this is that I have to know the name of 'Jmat' to get 
the description. 
Doing the 'functions' command is not very helpful since it lists all the 
functions and it is hard to find the name of one particular function.

The Mathenatica command 'usage'  is very helpful in that program.  It 
appends the user defined function to the set of all functions, so that 
one can search knowing only the first few letters of a user defined 
function. 
Thus, in Mathematica, I would only have to use
 Jmat::usage = "Jmat(f,x) gives the Jacobian matrix of the function 
f:R^m -> R^n";

Then,
 ?Jm*
would produce a list of all functions starting with 'Jm' and then
 ?Jmat
 would give the description of the usage of Jmat.

TIA for any ideas.
 -sen