Most materials we use are clearly visible and are sometimes accompanied by packaging or labels to leave us no doubt as to what we are working with. For reasons best known to those who created MicroSoft Windows, this is not the case with electronic data since, by default, the file-type extension is hidden from us. It is the file-type extension (e.g. .doc or .bmp) that we must look at to ‘see’ what material we are working with (unless of course we choose to examine the code itself - which would be analogous to taking a microscope to identify each timber variety!).