Return a list of all existing non-subsidiary coding systems.
If optional arg BASE-ONLY is non-nil, only base coding systems are
listed. The value doesn't include subsidiary coding systems which are
made from bases and aliases automatically for various end-of-line
formats (e.g. iso-latin-1-unix, koi8-r-dos).
List of coding systems.
Do not alter the value of this variable manually. This variable should be
updated by the functions `define-coding-system' and
`define-coding-system-alias'.