function id(oInterface) {
		var i,
			sPath = oInterface.getPath(),
			aResult;

		if (sPath) {
			return sPath.replace(rBadIdChars, ".");
		}
		aResult = [];
		// "probe for the smallest non-negative integer"
		for (i = 0; oInterface.getPath(i); i += 1) {
			aResult.push(oInterface.getPath(i).replace(rBadIdChars, "."));
		}
		return aResult.join("::");
	}
Custom formatter function to compute an unstable ID from the given interface's path(s).

@param {sap.ui.core.util.XMLPreprocessor.IContext} oInterface
  the callback interface related to the current formatter call
@returns {string}
  the resulting ID string value to write into the processed XML