Using https://mathematica.stackexchange.com/questions/30884/displaying-index-as-subscript-on-output-e-g-ci-c-i-with-notation-or I have often ended up wanting to define functions of annotated variables to better match my whiteboard mathematics.  Naively, I would want to do things like:
    
    f[z[bar]_] := z[bar]^2;
    relativez[z_, z[bar]_] := z / z[bar];

However, this doesn't work.    Obviously, I can do things like
    
    f[zbar_] := zbar^2;
    f[z[bar]]

But I would prefer to have it map to my math better if a simple variation of this pattern works.