The Computed Style function is display only, it does not allow editing of the values. According to W3C specifications, all properties should always be set, even if they have not explicitly been done so by the author of a page. Some properties may appear which are not part of the standards, usually of type -vendor-proprty-name. These are either for internal use, or testing of properties before implementation or standardisation is complete. They can safely be ignored.
This is useful for checking the properties you have set are doing what you think they do.