var targettag = new Array('p'); //get all tags for //

var sizes = new Array('10px','12px','14px','16px','18px','20px','22px','24px','26px');

var initialSize = 2;

function changeSize(IdTarget,action ){

  if (!document.getElementById) return

  var selected = null,size = initialsize,i,j,targettags;

  size += action;

  if ( size < 0 ) size = 0;

  if ( size > 6 ) size = 6;

  initialsize = size;

  if ( !( selected = document.getElementById( idTarget ) ) ) selected = document.getElementsByTagName( idTarget )[ 0 ];

  selected.style.fontSize = sizes[ size ];

  for ( i = 0; i < tagTarget.length; i++ ){

    tagsTarget = selected.getElementsByTagName( tagTarget[ i ] );

    for ( j = 0; j < tagsTarget.length; j++ ) tagsTarget[ j ].style.fontSize = sizes[ size ];

  }