Normal data blocks are light or dark green, unused blocks are yellow, and double-referenced blocks are red or pink. A blue tag name indicates that the tag references data outside the IFD (ie. the value size is greater than 4 bytes), and all data in the maker notes value block is underlined. Note that in TIFF images, image data appears as [unused], and is only dumped if it occurs before the meta information.
Currently, only EXIF and/or TIFF information is dumped. By default, all offsets are relative to the start of the TIFF header (as below). For a TIFF image this is at the start of the file, but for a JPEG image it is 6 bytes into the data of the APP1 Exif segment. However, this base offset can be specified on the command line with '-htmlDump#' (ie. '-htmlDump0' for absolute offsets), or via the API with the 'HtmlDumpBase' option.