Transparency Command Mockup

Quick links and legend:

The following is basically equivalent to Chimera1 transparency.

Usage:
transparency  spec  percent  [ frames  N ] [ target  string ]

The transparency command sets transparency to the specified percent, where 0% is completely opaque and 100% is completely transparent, without otherwise changing colors. The frames option indicates making the change gradually over N frames. Still not settled where the spec should go. Except for the frames option, this mockup is analogous to that for single-color assignment with the color command. See also: color

The target option allows acting on only a subset of the possible displays of a given atom, residue, etc. The string can be any combination of the following letters, without commas or spaces:

The default target is all but the last three (alscrnm), except further limited to just atoms/bonds and their associated labels and surface patches (als) when spec contains only explicit specifications of atoms by atom name, atom type, element, and/or atom attribute.

(These comments are essentially the same as for the color command)
Is this doable? By explicit specification I mean that although higher levels could be included in spec, all the “leaves” would be down to the atom level, for example:

   :48-56@ca
   #0@n,ca,c,o
   /A:48@NZ/B:200@OD1
   ligand z<5 & S