[MarkSheppard]

A compressed section is made up of multiple interspersed compressed and uncompressed run-length encoded data blocks.

Each run-length coded data block consists of:

[N] a run-length coding byte (RLB)
[b] one or more data bytes.

The Run Length Coding Byte (RLB) is the trigger that tells us what type of data block it is:

If the RLB is equal to or less than 127, it's a uncompressed run-length coded (URLC) data block, which is used for sequences with mixed values:

[N] The RLB indicates the number of data bytes that follow, which can be from 1 to 127 bytes.
[b] Individual Data Bytes that can be copied/edited as/is.

If the RLB is equal to or greater than 128, it's a compressed run-length coded (CRLC) data block, which is used for large sequences of identical data bytes to save space.

[N] The RLB indicates the number of identical data bytes that follow from 1 to 127 bytes.

BIG IMPORTANT NOTE:
To get the true RLB for a CRLC block, you need to subtract 128 from the initial RLB. For example, if your CRLC has a RLB of 250, it's true length is actually: 250 – 128 = 122 Byte RLB. (This is what tripped me up; I was assuming 250, 0 meant 250 bytes of identical 0 value.)

[b] Data Value for All the Bytes in this block. The decompressed data is the sequence of N times the data byte B.

A visual representation of the typical sequence of a compressed data block is attached.

RED: Section Header. 4-byte Header Marker (37 0 0 0) followed by compressed size (33 0 0 0) and the compressed flag (1).

GREEN (Uncompressed) and BLUE (Compressed) Blocks You can see how the RLB says 16 bytes, followed by 16 bytes, then you have a compressed block of 86 bytes (214 - 128 = 86) with a value of zero; and so on so on.