It's possible to customize the YAML editor by creating a custom .yaml.liclipseprefs file.
The customization must be done per-project by creating a file such as:
project/.settings/.javascript.liclipseprefs
or
project/.javascript.liclipseprefs
The default file considered if none is provided is:
# Option determining whether syntax errors should be collected (with snakeyaml)
collect_errors: true
See:
https://code.google.com/p/snakeyaml/wiki/Documentation#YAML_syntax
for more details.