Define "visible" about emergence.js

[dmethvin]

Oh z-index as well, since something could be totally covered by an element with a higher z-index.

[xtianmiller]

Hey @dmethvin,
You're correct; it simply determines if a displayed element is within the viewport, and within the criteria set within the options. The other properties are not tied to emergence visibility because that'd hard to measure and account for everything based on the complexity of some layouts—but you may also want to update some these properties for animation sake so it gets mirky if you start tracking them.

The goal is to make the plugin as flexible as possible for most scenarios. For example, if an element is in a slider that's off-canvas due to transform, you can use emergence.engage() to refire based on click, swipe, or other triggers.

This is good feedback for documentation I'll make a note to update the README on next release.