_handleSource( string, errorLine ) {

		const lines = string.split( '\n' );
		const lines2 = [];

		const from = Math.max( errorLine - 6, 0 );
		const to = Math.min( errorLine + 6, lines.length );

		for ( let i = from; i < to; i ++ ) {

			const line = i + 1;
			lines2.push( `${line === errorLine ? '>' : ' '} ${line}: ${lines[ i ]}` );

		}

		return lines2.join( '\n' );

	}
Formats the source code of error messages.

@private
@param {string} string - The code.
@param {number} errorLine - The error line.
@return {string} The formatted code.