//Specify affected tags. Add or remove from list:
var tgs = new Array( 'p', 'h1', 'h2', 'h3', 'h4', 'h5');
var adjuster = 2;

function ts( trgt,inc ) {
    if (!document.getElementById) return
    var d = document,cEl = null,i,j,cTags;
    
    if (!( cEl = d.getElementById( trgt ) ) ) cEl = d.getElementsByTagName( trgt )[ 0 ];

    for ( i = 0 ; i < tgs.length ; i++ ) 
    {
        cTags = cEl.getElementsByTagName( tgs[ i ] );
        for ( j = 0 ; j < cTags.length ; j++ )
        { 
            if(cTags[ j ].style.fontSize) {
                //if element has a defined size, get the int val of that
                var s = parseInt(cTags[ j ].style.fontSize.replace("px",""));
            } else {
                //if element doesn't have a defined size we default
                var s = 14;
            }
            
            if(inc == 1){
                //increase size by
                s += adjuster;
            }
            else if(inc == -1){
                //increase size by
                s -= adjuster;
            }

            //alert(cTags[ j ].style.fontSize);
            cTags[ j ].style.fontSize = s+"px";
        }
    }
}