src/vs/platform/configuration/common/configurationRegistry.ts/validateProperty
export function validateProperty(property: string): string | null {
	if (!property.trim()) {
		return nls.localize('config.property.empty', "Cannot register an empty property");
	}
	if (OVERRIDE_PROPERTY_REGEX.test(property)) {
		return nls.localize('config.property.languageDefault', "Cannot register '{0}'. This matches property pattern '\\\\[.*\\\\]$' for describing language specific editor settings. Use 'configurationDefaults' contribution.", property);
	}
	if (configurationRegistry.getConfigurationProperties()[property] !== undefined) {
		return nls.localize('config.property.duplicate', "Cannot register '{0}'. This property is already registered.", property);
	}
	return null;
}