24-bit colors question

[Yakov Lerner]

On 3/20/06, Marc Lehmann <schmorp at schmorp.de> wrote:
> On Sun, Mar 19, 2006 at 11:38:44PM +0300, Yakov Lerner <iler.ml at gmail.com> wrote:
> > I found escape sequences in the doc. Can I have clarification regaring these:
> >            Ps = 10         Change colour of text foreground to Pt
> >            Ps = 11         Change colour of text background to Pt
>
> Yes, and the other sequences that change the other color indices.
>
> > 1. Does what you said mean that X color names can be used
> > as Pt in Ps = 10 and PS=11 sequences ?
>
> Yes, in addition, the ones supported by rxvt-unicode, too (rgba:///)

I am planning to make patch for vim to enable vim
use of this unique feature of  urxvt, the 24-bit rgb colors. I have
some questions about how vim can best recognize that terminal
has this capabilty.

1. How do you suggest that application (vim in this case) detect
that terminal is capable of accepting 24-bit rgb values, and which
escape-sequences it shall use.
Which approach do you recommend:

a) Via terminfo ? Does rxvt-unicode have terminfo entry that signals
to the application that terminal accepts X11 RGBs values as colors ?
Which entries are those ? Or,

b) to hardcode the TERM value into vim, the to hardcode
and color-setting escape-sequences ? (vim already uses
hardcoded sequences for some terminal types) ? Or,

c) shall vim rely on querying ? (vim always uses query on xterm.)
Can vim reliably identify urxvt by querying ?

2.  What does these remarks mean in the 'urxvt command sequences':

      Ps=10 ...'NB: may change in the future'
      Ps=11 ...'NB: may change in the future'

Does this mean there are alternative equivalent commands that are
stable ?

3.  Is there any build configuration, or runtime-configuration, or a
platform where urxvt won't accept or won't render rgb values ? If yes,
how can vim recognize such situation under urxvt (quering ? terminfo ?)

Thanks
Yakov