Support for full CSS selectors in VFL

[mountainstorm]

@horizontal |[#smartFindGroups]~| in(#search > .panel-body)

As a general rule the number of rules needed is huge - a visual editor would make this much easier!

[d4tocchini]

Currently, complex CSS selectors work more reliably with rulesets, so you could accomplish this with,

#search > .panel-body {
  @horizontal |[#smartFindGroups]~| in(::);
}

Yeah, fully specifying a constraint layout can be verbose, and though I like the idea of a visual editor, not convinced it will make complex situations any easier, see. Better debugging & visualizing the constraints is something more achievable in the short term.

Another problem is the lack of higher level abstractions for grid-based layouts. We should be able to constrain DOM elements to the "Virtual Elements" of a grid, like a grid-col or grid-area, which could be constrained like normal elements but wouldn't exist in the DOM. I'm currently working on Virtual Elements and a constraint-based implementation of the Grid Layout Module. This will allow a workflow of quickly setting up a grid for different adaptive scenarios, and then aligning elements to the grid, thus alleviating the tedium of constraining every element.