Highlighting Available Dropzones on click

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Hi,

I'm working through some thoughts on the c5.7 interface. One thing I would like to experiment with is making the available locations to drop a block highlight when the block is clicked in the "Add Block" panel. So, instead of click and drag to place the block, a simple click and release (not sure of the triggering action right now) would highlight the available areas.

I am having difficulty finding the class associated with these areas that highlight when you drag "near" them. So, if anyone could point me to the right class I would appreciate it.

Also, if anyone knows the function that fires to cause the highlighted area, I'd love to know that also.

I'm experimenting now but, if I like what comes of it, I will present it to the community for consideration.