That's not all folks.....
As promised, here is OCLC’s version of the MARC standard:
I don’t tend to use this one that much because it is generally less up to date and also I find it a little harder to navigate. However, it does have some strengths so it may be worth having a look at it sometime. It gives a slightly different explanation or definition of the MARC tag that helps clarify why it might be used. A very useful feature is that this website lists some of the odd local or OCLC specific tags which are not part of the “official” standard. An example is the 099 tag which can be found in this version of the standard. In short, the OCLC version of the MARC Standard is much more complete but not my first place to look because it is not as easy to tell which tags are actually part of the international standard and which are local and because it is less up to date. However, because of richness of the information it contains, it is a valuable resource to use and is often the second place I look when seeking information about MARC tags.