No, but you can use fcount() and field() in a FOR loop to figure out what fieldnames are in the KEY().

lparameter tcExpression
local lcFields
for lnI = 1 to fcount()
    if at(field(lnI), upper(tcExpression))
       if not empty(lcFields)
          lcFields = lcFields + ','
       endif
       lcFields = lcFields + field(lnI)
    endif
endfor
return lcFields

>How can I get the field name associated with an index tag.
>
>For example: the KEY() function returns the index expression, but is there a function to return the field name that the tag belongs to?
>
>If I: INDEX ON UPPER(myfield) TAG mytag, ?KEY('mytable', 1) returns UPPER(myfield). I only want the field myfield returned.
>
>Thanks,
>
>Jerryt