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.
.project
.directory
.pytest_cache
.cache
.coverage_full
syntax: regexp
^tests/.*/build$
^.idea/.*
syntax: regexp
^.*\.pyc$
syntax: regexp
^.*~$
syntax: regexp
^.*\.swp$
bug_report.*\.txt
i18n/.*.new$
revision
doc/_build
doc/locale