Re: substitute-command-keys does not preserve text properties

[Richard M. Stallman]

    If you pass a string with text properties through substitute-command-keys,
    the returned string does not preserve the text properties of the original
    string if any command keys were substituted.  If no substitutions were
    made, properties are preserved (I guess the original string is returned).

    This behaviour may be ok, but it is not documented.

I think it is not worth changing the behavior; could you document it?