src/index.js/normalizeOptions
function normalizeOptions ( options ) {
	return assign( {
		generate: 'dom',

		// a filename is necessary for sourcemap generation
		filename: 'SvelteComponent.html',

		onwarn: warning => {
			if ( warning.loc ) {
				console.warn( `(${warning.loc.line}:${warning.loc.column}) – ${warning.message}` ); // eslint-disable-line no-console
			} else {
				console.warn( warning.message ); // eslint-disable-line no-console
			}
		},

		onerror: error => {
			throw error;
		}
	}, options );
}