Re: Doc: improve doc on markup command writing (issue157133)

[dak]

It would make sense to apply <URL:http://codereview.appspot.com/160048>
first and make this patch work on top of that.

There may be cases where a separate property-bind like this is useful in
called routines, and the markup commands from the mentioned patch might
make use of it for implementing #:properties.  However, a separate
property-bind function can't do the job of entering the properties and
their defaults into the command reference.

For this reason, it is probably not a good idea to encourage users to
use a macro like this in markups defined with define-markup-command.
They would need to be rewritten in order to get the properties mentioned
in the command reference.

Since the above-mentioned patch does not provide user-level
documentation, it would make sense to adapt your patch here for
documenting the functionality provided by the above-mentioned patch of
mine.

http://codereview.appspot.com/157133