KEKS can store various primitive scalar types (strings, integers, ...)
and container types (lists, maps, ...). Serialisation process is just
emitting the TLV-like encoding for each item recursively.
Possible values for the tag (also see the [encoding/FullTable]):

dec | hex | bin      | vlen |
000 | 00  | 00000000 | 0    | [encoding/LIST]'s EOC
001 | 01  | 00000001 | 0    | [encoding/PRIM] NIL
002 | 02  | 00000010 | 0    | [encoding/PRIM] FALSE
003 | 03  | 00000011 | 0    | [encoding/PRIM] TRUE
004 | 04  | 00000100 | 16   | [encoding/HEXLET]
... | ... | ...      | ...  | ...
008 | 08  | 00001000 | 0    | [encoding/LIST]
009 | 09  | 00001001 | 0    | [encoding/MAP]
010 | 0A  | 00001010 |
011 | 0B  | 00001011 | 8+~  | [encoding/BLOB]
012 | 0C  | 00001100 | 1+~  | + [encoding/INT]
013 | 0D  | 00001101 | 1+~  | - [encoding/INT]
... | ... | ...      | ...  | ...
016 | 10  | 00010000 | 2    | [encoding/FLOAT] 16
017 | 11  | 00010001 | 4    | [encoding/FLOAT] 32
018 | 12  | 00010010 | 8    | [encoding/FLOAT] 64
019 | 13  | 00010011 | 16   | [encoding/FLOAT] 128
020 | 14  | 00010100 | 32   | [encoding/FLOAT] 256
... | ... | ...      | ...  | ...
024 | 18  | 00011000 | 8    | [encoding/TAI64]
025 | 19  | 00011001 | 12   | [encoding/TAI64] N
026 | 1A  | 00011010 | 16   | [encoding/TAI64] NA
... | ... | ...      | ...  | ...
075 | 4B  | 01001011 | 15   | [encoding/MAGIC]
... | ... | ...      | ...  | ...
128 | 80  | 10LLLLLL | 0    | Binary [encoding/String] len=0
... | ... | ...      | ...  | ...
188 | BC  | 10111100 | 60   | Binary [encoding/String] len=60
189 | BD  | 10111101 | 1+~  | Binary [encoding/String] len of 8b
190 | BE  | 10111110 | 2+~  | Binary [encoding/String] len of 16b
191 | BF  | 10111111 | 8+~  | Binary [encoding/String] len of 64b
192 | C0  | 11LLLLLL | 0    | UTF-8 [encoding/String] len=0
... | ... | ...      | ...  | ...
252 | FC  | 11111100 | 60   | UTF-8 [encoding/String] len=60
253 | FD  | 11111101 | 1+~  | UTF-8 [encoding/String] len of 8b
254 | FE  | 11111110 | 2+~  | UTF-8 [encoding/String] len of 16b
255 | FF  | 11111111 | 8+~  | UTF-8 [encoding/String] len of 64b