//Specify affected tags. Add or remove from list:
var tgs = new Array('a', 'td', 'tr', 'p', 'span', 'font');
//Specify spectrum of different font sizes:
var szs = new Array('10px', '11px', '12px', '13px', '14px', '15px', '16px');
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];
    }
}