Paul> The current code is broken, definitely. And if tag sets do Paul> refer to devices, then I think that my patch is ok. But if Paul> tag sets involve MULE ... <shudder> No, no. I cannot tell a lie. They don't involve Mule. There are two things that you need to do (in my off-the-cuff opinion). One is when you have a set of functions that manipulate specifiers, you should anticipate that callers---written by others, possibly in the future---might want to use tags as well and provide an interface (eg, an optional argument) to pass a tag set. Then when you call the specifier functions you do something like (defun my-func (value &optional tag-set-arg) (if (intersect tag-set-arg tags-mutually-exclusive-with-mine) (if this-is-a-disaster (error "Called with incompatible tags!") (do-nothing-clean-up-and-exit)) (manipulate-specifier specifier value (cons my-tag tag-set-arg) ...))) Try to arrange that functions compute what they need to do from a specifier, rather than using (cond ((eq tag 'x) (x-do-something ...)) ((eq tag 'mswindows) (mswindows-do-something ...)) ...) Specifiers often can do that for you magically. If you do those two things, then other code written to use specifiers should pretty automatically work right. Of course, you don't always need to do them if you're pretty sure they're only auxiliary functions for your own code; then you should document them as internal, interface subject to change, please use XYZ instead, etc etc. Jan claimed (if I read it right) that specifiers are inefficient; maybe they are. So keep an eye on performance. But specifiers were designed to do very complex manipulations of these types as efficiently as possible; doing switching on device type and the like at the Lisp level should reach decreasing returns fairly early on as complexity of the condition increases. -- University of Tsukuba Tennodai 1-1-1 Tsukuba 305-8573 JAPAN Institute of Policy and Planning Sciences Tel/fax: +81 (298) 53-5091 __________________________________________________________________________ __________________________________________________________________________ What are those two straight lines for? "Free software rules."