Accept CSS strings in addition to CSS object literals

[lederer]

For those used to composing CSS, it can be cumbersome to compose object literals. We should consider accepting properly formed CSS strings for transition, showTransition, hideTransition, as an alternative to CSS object literals. The primary purpose is the same: to express the hidden CSS state of the item.

Some intertwining considerations:

• Would it still be possible to provide per-property timings when passing a string instead of an object? How?
• What happens if they include transition as one of the CSS properties in the string? Ignore it? Defer to it?
• Should we also allow the string expression of the CSS transition property via a distinct setting (eg, CSSTransitionProperty), so they can author their own timings via a string rather than having it automatically assembled from our various symmetric, asymmetric, and per-property timing settings?

Overall this seems like too much complexity and ambiguity. But the pull of authoring CSS as… CSS, can be quite strong for those proficient in it.