Wildcard tagging

[gicmo]

Currently the position and extends of a Tag need to match the referenced DataArrays. For certain cases it would make sense to have the Tag only specify a subset of the dimensions. For example a region of interest in an image stack, N 2-d images taken at various points in time (x, y, t), would be specified in 2d (the image plane) and would apply to all the images in the stack. Wildcard, because the Tag basically would be (x, y, *).