To answer my own question, after experimentation:

\index[key]{form::entry}
with
\setupregister[index][form][textstyle=\hskip1em]


A.

On Sun, Mar 18, 2012 at 12:38 PM, Alan Bowen <bowenalan03@gmail.com> wrote:
Sorry: My effort escaped without a subject line.


In placing the heads and subheads of indices, \index defaults to

Head    locator
Head
    subhead    locator

I need to get the subhead without repeating the Head, as in
Head    locator
    subhead    locator

How can I do this? Is there some documentation on this that I can read? 

Alan