Will add copyright header.  I'll add some docs for the various concepts.

A partition table is an array of partitions.

An individual partition is made up of contiguous sectors in a device.

A chip descriptor describes the properties of an individual flash device.  This includes a full description of the sizes of each sector in that device.  Not all sectors have to be the same size in a flash device (eg. STM internal flash).  Rather than making a big array of sector sizes, I use a simple run-lengh-coding that allows a compact representation of adjacent sectors that have the same lengths.  For most SPI flash devices, this compresses to a single block since all sectors have the same size on most SPI flash devices.

Arena is really a logfs concept rather than a partition concept so wouldn't be documented here but I can add something to logfs about that.