Attempt to workaround problem reported about empty plc.xml after unrelated crash. Now, if etree model is corrupted in a way tostring() would generate an empty string, exception prevents saving.
IEC 61131-3
===========
IEC-61131 is a normative document provided by the standards organization IEC
(International Electrotechnical Commission) and describing a standard for
implementing programmable controllers.
The part 3 of this document (commonly named IEC 61131-3) specifies syntax and
semantics for programming language for programmable controllers. Beremiz
implements all the languages described in this document.
http://www.iec.eu
PLCopen TC6
===========
PLCopen is a vendor- and product-independent worldwide association defining
international standards for various topics related to control programming.
For this purpose, PLCopen has 6 technical committees.
The goal of the sixth committee (TC6) is to define a standard file format,
based on XML, for exchanging programmables controllers programmed using
IEC 61131-3 languages. Beremiz uses this file format for saving the PLC
programs of projects.
http://www.plcopen.org