diff --git a/BizHawk.Emulation.Cores/Consoles/PC Engine/CDL File Format.txt b/BizHawk.Emulation.Cores/Consoles/PC Engine/CDL File Format.txt
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+A "string" is an LEB128 encoded number which is the number of bytes
+in the string, followed by that many bytes of UTF-8 character data.
+
+A "number" is a little endian 32 bit integer.
+
+File format is as follows:
+
+number NumberOfBlocks: number of memory areas represented in this file
+
+For each block:
+
+string BlockName: identifying name of the block.
+number bytelength: length of the block in bytes.
+byte data[bytelength]: one byte of information for each byte in the original block.
+
+
+
+The BlockNames are:
+
+ROM
+  HUCard ROM, or syscard bios ROm
+
+Cart Battery RAM
+  32K of battery backed ram in the Populous cart
+
+Super System Card RAM
+  192K of ram in the super system card
+
+TurboCD RAM
+  64K of ram in the turboCD
+
+BRAM
+  8K of TurboCD backup RAM.  The actual RAM is smaller, but the CDL will record all
+  activity in that 8K region.
+
+Main Memory
+  8K or 32K (SGX) of main memory
+
+MMIO
+  8K of space in block ff, containing system IO ports.
+
+UNKNOWN
+  8K long area which any unknown block maps to.
+
+
+Each byte has 8 bits of flags on what the byte has been observed to do:
+
+// was fetched as an opcode
+Code = 0x01,
+// was read or written as data
+Data = 0x02,
+// was read and used as a pointer to data via indirect addressing
+DataPtr = 0x04,
+// was read or written as stack
+Stack = 0x08,
+// was read or written as data via indirect addressing
+IndirectData = 0x10,
+// was read and used as function pointer
+// NB: there is no "IndirectCode"; all code is marked simply as code regardless of how it is reached
+FcnPtr = 0x20,
+// was used as a source (either initial or during the loop) of a block xfer
+BlockFrom = 0x40,
+// was used as a destination (either initial or during the loop) of a block xfer
+BlockTo = 0x80
+
+