Well, virtually anything is possible, but the question then becomes which of those broad range of possibilities should be implemented, and at what cost. Two of the biggest costs are, first, the cost of learning wheels within wheels, fractal complexity, and then, second, decoding what someone (perhaps even yourself a few weeks ago...) has done using such complexity. Good examples of the costs are the various text editors out there catering to niche interests that allow infinite customization and personal macros for everything, so people who use them constantly might customize them mightily, only to discover that after coming back from a one-week vacation they are completely unable to use their own, "home" editor. In the case of wheels within wheels application of transparency, sure, you can get exactly the effect you want in some particular case, but then perhaps even you, yourself, might have to work to decode exactly what the visual display is all about, only towards the end drilling down into an "aha... I have individual transparency set per object based on this field..." moment. We can see those factors in play right now in 9 when you consider a) formatting, and b) formatting with per-object style overrides. a) is straightforward to explain and to understand, and it is very WYSIWIG in terms of understanding what style in a given layer is about. One layer, one style, is an easy model to grasp and to apply. Use layers to group whatever you want into whatever constellations of styles that you want. b) is much more complicated for beginners to grasp, much more difficult to explain, and, potentially, staggeringly more complex to decode what is going on in a visual display. When any one object can modify some part or all of a style for a layer, just for itself, you get into a true labyrinth of possibilities. Another example is the "every window can have its own selection" notion originally introduced in 9 and then later withdrawn. It was a case of a bridge too far in terms of possibilities, where a return to the constrained, simpler situation of one selection for every component based on a given table was a true example of the adage, "less is more." I feel that way about per-object formatting as well. I don't like style overrides at all for that reason, but I understand that it is one of those things where there is no point in arguing with the market. Some things people have to learn the hard way, for themselves. I strongly recommend people make the effort to think in terms of "normal form," to borrow a DBMS concept, where if classes of objects are distinguished enough to use different styles they probably should be organized as different layers, that is, distinguished into different data bins as well. Yes, that does take a bit more effort initially at organization than just forcing a color here and there on the fly. But it is effort that pays off over and over in the future while the forcing of appearance using things like style overrides is borrowing now at what often ends up being a vicious payback rate later on. All the above come together with special ferocity when leveraging 9, because 9 makes it so easy to introduce endless, wheels within wheels complexity. 9 has so much raw power internally that intricate chains of display rules which simply could not be possible in classic GIS technology like Arc, Q or 8, where they would be too slow, are perfectly doable in 9. So you don't have the constraint of being forced into a better, "less is more" interface, and can make it as opulently baroque as you like. That means the only limitation we have on achieving a "less is more" balance is the good taste and self-restraint we ourselves, as a community, can summon. :-) So, anyway, I'd close this mini-rant with the observation that not everything that is possible should be done. We should always really think hard about the cost of teaching beginners some new intricacy, to consider if there really is a need for that intricacy, and to consider how maintainable/understandable the intricacy would be in practice in a project months or years after we did something intricately clever. Hope that helps!
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