//Specify affected tags. Add or remove from list:
var tgs = new Array( 'div','span','td','a' );

//Specify spectrum of different font sizes:
var szs = new Array( 'xx-small','x-small','small','medium','large','x-large','xx-large' );
var startSz = 3;

function ts( trgt,inc ) {
  if (!document.getElementById)
    return;
  var d = document,cEl = null,sz = startSz,i,j,cTags;
  sz += inc;
  if ( sz < 0 ) sz = 0;
  if ( sz > 4 ) sz = 4;
  startSz = sz;
  if ( !( cEl = d.getElementById( trgt ) ) )
      cEl = d.getElementsByTagName( trgt )[ 0 ];
  cEl.style.fontSize = szs[ sz ];

  for ( i = 0; i < tgs.length; i++ ) {
     cTags = cEl.getElementsByTagName( tgs[ i ] );
     for ( j = 0; j < cTags.length; j++ )
        cTags[ j ].style.fontSize = szs[ sz ];
  }
  window.parent.document.getElementById("iframe_corpo").height = document.getElementById("tamanho").scrollHeight + 140;
}