This is for executing arbitrary interaction and verification logic on
a given view. Only the accessibility label can be specified, as
verification against the traits and value can be done manually on the
view in the execution block.
If the element is not visible, the UIView will probably not exist and the
executionBlock will get the UIView that is visible and nearest to the
accessibility element in the hierarchy. This is not easy for the block to
predict and deal with, so use |_accessibilityElementWithLabel:| to make the