//Specify affected tags. Add or remove from list:
var tgs = new Array( 'div','td','tr', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'p', 'a');

//Specify spectrum of different font sizes:
var szs = new Array( '8px','9px','10px','12px','14px','16px','18px' );
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 > 6 ) sz = 6;
		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 ];
	}
}