Figure out `placeholder` in constraint.

[KingOfBrian]

There is a placeholder key on constraint. I'm not sure what this actually does. Very often it won't have enough information to generate a valid constraint and can cause failures.

[drumnkyle]

Placeholder is to just show in interface builder but not actually used at runtime. I think you can just ignore the value.

[KingOfBrian]

Nice, thanks @drumnkyle ! Have you seen symbolic? I'm ignoring it at the moment and creating the constraint anyway.

[drumnkyle]

@KingOfBrian I'm not sure what symbolic is. Haven't seen it much. Sorry.