文本域中焦点处插入字符串
el代表文本域对象，myvalue代表要录入的字符串。只适用于文本域中焦点追加字符串

function insertAtCursor(el, myValue) {    //IE support     if (document.selection) {         el.focus();         sel = document.selection.createRange();         sel.text = myValue;     } else if (el.selectionStart || el.selectionStart == '0') {        //MOZILLA/NETSCAPE support         var startPos = el.selectionStart;         var endPos = el.selectionEnd;         el.value = el.value.substring(0, startPos) + myValue + el.value.substring(endPos, el.value.length);     } else {         el.value += myValue;     } }