pcb-rnd - user manual 
 7.1 IO plugins 
 7.1.2 io_pcb 
Historically geda/PCB is the predecessor of pcb-rnd, but pcb-rnd has
switched native file format during the big data model rewrite (2016..2017).
This means the old geda/PCB file formats (board and element) are supported
only as alien file formats, with the usual alien format limitations.
At the moment pcb-rnd supports loading files up to geda/PCB version 4.3
(file version 20180318). This includes loading the latest additions of
blind/buried vias, center-specified pads and mask value in routing style.
When saving in this format, pcb-rnd will pick a much older format version,
see limitations below.
Extras in pcb-rnd:
	-  minor bugfixes so that numeric roundings on corner cases are better
	
-  unlike geda/PCB, pcb-rnd won't crash on invalid bbvia span values but throw an error message with the coords and load the via as thru-hole
	
-  pcb-rnd can save with different units
	
-  pcb-rnd makes an effort to preserve the unit style so a load-save operation causes less changes to the file than in geda/PCB
	
-  pcb-rnd has better support for ancient (pre-2000) file versions
Limitations in pcb-rnd:
	-  saving files: the newest geda/PCB file format version pcb-rnd can save is, 20100606; that already has polygon holes but:
	
		-  no center-defined pads so pad format is converted to line-based (in fact geda/PCB 4.3 also does this conversion on save)
		
-  no blind/buried vias
		
-  no mask value in routing style