code: private Dimensions computeVal(final String propName) {
  		final String property = definition.getProperty(propName);
  		if (property == null) {
  			throw new IllegalArgumentException("Could not find property " + propName);
  		}
  		return Dimensions.fromString(property);
  	}
docs: Computes a val from a property name. The string contained in the property
  must have a format that can be parsed by the
  {@link Dimensions#fromString(String)} method.
  
  @param propName
  the property containing the val to compute
  @return a {@link Dimensions} created from the string contained in the
  property