按字符数控制：
<textarea name="gbContent" style="width: 500px; height: 200px;"
onkeyup="if(this.value.length>2000) this.value=this.value.substr(0,2000)"
onkeydown="if(this.value.length>2000) this.value=this.value.substr(0,2000)"
onblur="if(this.value.length>2000) this.value=this.value.substr(0,2000)"
onpropertychange= "if(this.value.length>2000) this.value=this.value.substr(0,2000)"></textarea>
按字节数控制：
<textarea cols="50" id="description" name="userModel.description" rows="5"
onkeydown="key1=this.value;value1 = key1.replace(/[\u4e00-\u9fa5]/g,' ');if(value1.length>500) this.value=this.value.substr(0,500)"
onkeyup="key1=this.value;value1 = key1.replace(/[\u4e00-\u9fa5]/g,' ');if(value1.length>500) this.value=this.value.substr(0,500)"
onblur="key1=this.value;value1 = key1.replace(/[\u4e00-\u9fa5]/g,' ');if(value1.length>500) this.value=this.value.substr(0,500)"
onchange="key1=this.value;value1 = key1.replace(/[\u4e00-\u9fa5]/g,' ');if(value1.length>500) this.value=this.value.substr(0,500)"></textarea>