According to this MS guideline http://msdn.microsoft.com/en-us/library/ms229043.aspx, if name of a member starts with two-letter acronym, both letters should be uppercase. The first letter of next word is also uppercase, so, it should be IOStream, for example. When camel case convention (CamelCaseElementNameConvention) is applied, such name should definitely be turned into ioStream, not iOStream.