Tag Tree

RSB uses an XML-like tag system called the "tag tree" for internal organization. This system is designed for both extensibility and backwards compatibility. Unlike XML though, RSB is a binary format. Each tag has a constant i8 value.

Tags come in two types: matched and unmatched. Matched tags affect everything between an opening and a closing tag. They are generally used for things of varying length or things whose length is likely to change in future versions of the specification. Unmatched tags affect a certain fixed number of bytes after a single tag. They can save a bit of space in some places but are much less extensible, so they are used relatively sparingly.

With matched tags, there must be a 1:1 matchup between start and end tags. Additionally, before an outer block can be closed, all of its nested inner blocks must be fully closed, e.g., the following is not allowed:

X_START Y_START X_END Y_END
                |     |
                |     doesn't make sense outside of X block
                |
                X closed before inner Y

Skip Tags: Fixed and Variable

Skip tags are used to skip a certain number of bytes when searching for tags. This is useful when storing raw numerical information that may unintentionally contain tag bytes which should not be read.

Fixed Skip Tags

SKIP_N instructs the interpreter to not search for tags within the following N bytes.

SKIP_2 N N Y

N here means that a byte is skipped during tag searching and Y means that it is checked for tags. SKIP_2, of course, skips 2 bytes.

Variable Skip Tags

SKIP_U8 (-123): Read the u8 value of the next byte. Add 1 and do not search for tags for that number of bytes after it. For example, one may see the following in a file:

SKIP_U8 3u8 N N N N Y

N and Y mean the same as above. SKIP_U8 can skip up to 256 bytes.

SKIP_U16 (-122): Read the u16 value of the next 2 bytes. Add 1 and do not search for tags for that number of bytes after them. For example, one may see the following in a file:

SKIP_U16 4u16 N N N N N Y

Note here that 4u16 takes up two bytes. SKIP_U16 can skip up to 64KiB.