NAME

       Data::CompactReadonly::V0::Format - a description of CompactReadonly data format, version
       0.

NOTATION

       Bytes with values that are printable ASCII will be shown as a single ASCII character.
       Otherwise bytes will be shown either in hexadecimal - 0xAB - or binary - "0b01010101".

       When appropriate bit-fields will be shown in binary "0b100".

       Bytes will be separated by spaces, bit-fields within a byte by hyphens - "0b11-0000-00".

ENDIANNESS

       All internal structures are big-endian.

FILE HEADER

       The file header is five bytes long. The first four serve to identify the file type:

           C R O D

       The fifth is a bit-field that encodes in the most significant five bits the file format
       version number, and in the least significant three bits encodes the pointer length that is
       used in the file. Values from 0 to 7 correspond to pointer lengths from 1 to 8 bytes.

       The five byte header is immediately followed by the root node.

       Version number 31 (0b11111-XXX) is reserved for future use.

NODES

       Data is encoded in nodes, which can be of several types. The types fall into two
       categories:

       Scalar types
           Scalars encode a simple value. That can be a number or the NULL value. The five
           integer numeric types are also available as NegativeByte, NegativeMedium and so on.

           Byte - 8 bit integer
           Short - 16 bit integer
           Medium - 24 bit integer
           Long - 32 bit integer
           Huge - 64 bit integer
           Float64 - 64 bit IEEE754 double-precision
           Null
           True
           False
       Collection types
           Collections encode multiple values.

           Text
               Encodes a list of characters - that is, a string.

           Array
               Encodes a list of nodes, which can themselves be of any type.

           Dictionary
               Encodes a list of key-value pairs, the keys being strings or numbers and the
               values being nodes of any type. The keys must be stored in ASCIIbetical order.
               Note that while the use of numeric types is *permitted* for keys it is not
               recommended, as you may run into problems finding floating point keys because of
               the usual floating point imprecision issues.

       Each node is encoded as a type header occupying from 1 to 9 bytes, followed by data if
       necessary

   NODE TYPE HEADERS
       The type header consists of a type specifier followed by up to 8 bytes telling us how much
       data is in the node. The type specifier is a bit field.  The first two bits will tell us
       whether the node is a collection or not.

           0b00 - Text node

           0b01 - Array node

           0b10 - Dictionary node

           0b11 - it's not a collection, it's a scalar node

       The next four bits tell us, for scalar nodes, the type, or for collection nodes some of
       them tell us what type is used to encode the collection's length. Only Byte, Short,
       Medium, and Long are valid for lengths.

           0b0000 - Byte (valid as a length)        0b0001 - NegativeByte

           0b0010 - Short (valid as a length)       0b0011 - NegativeShort

           0b0100 - Medium (valid as a length)      0b0101 - NegativeMedium

           0b0110 - Long (valid as a length)        0b0111 - NegativeLong

           0b1000 - Huge                            0b1001 - NegativeHuge

           0b1010 - Null

           0b1011 - Float64

           0b1100 - True

           0b1101 - False

       Any unspecified bits or combinations of bits are reserved for future use. Unspecified bits
       should be set to zero if you want your data to be compatible with future versions.

   NODE DATA
       NUMERIC NODES

       The header is followed by the appropriate number of bytes of data.

       NULL, TRUE and FALSE NODES

       These are just a header.

       TEXT NODES

       The header is followed by the appropriate number of bytes to encode the text's length,
       followed by that many bytes of text. Note that text lengths are stored in bytes but text
       is actually encoded in UTF-8. So the 3 character string "北京市" is stored as the 9 bytes:

           北: 0xE5 0x8C 0x97    京: 0xE4 0xBA 0xAC    市: 0xE5 0xB8 0x82

       and the entire node would be the 11 bytes:

           0b00-0000-00:  this is a Text node, with the length stored in a Byte
           0x09:          the length of the text
           0xE5 ... 0x82: nine bytes of text

       ARRAY NODES

       The header is followed by the appropriate number of bytes to encode the number of elements
       in the array, "N". Zero obviously means an empty array. That is immediately followed by
       "N" pointers of the size specified in the database header. Each pointer is the location in
       the file of another node, which can be of any type.

       DICTIIONARY NODES

       The hader is followed by the appropriate number of bytes to encode the number of elements
       in thedictionary, "N". Zero means an empty dictionary. That is immediately followed by "N"
       pairs of pointers of the size specifed in the database header. The first pointer in each
       pair must point to a Text or numeric node which will be used as a key for looking up
       values. The second pointer in each pair points to the value, which can be any type of
       node. The pointers to keys must list them in ASCIIbetical order. If they are out of order
       some elements may not be able to be found.