docs: function addFilePrefix( path, prefix ) {
    if ( typeof prefix === 'undefined' ) prefix = '@';
  
    var separatorPosition = path.lastIndexOf( '/' );
    if ( separatorPosition < 0 ) {
      // Let's try with Windows separators.
      separatorPosition = path.lastIndexOf( '\\' );
    }
    var filenameStart = separatorPosition > -1 ? separatorPosition + 1 : 0;
    var result = path.substr( 0, filenameStart ) + prefix + path.substr( filenameStart );
    return result.replace( /\\/g, '/' );
  }