Hi,
There are two facts here. First, tag thtmlb:button does not have control over the length, it will be changed based on the text length. And unfortunately we do not have a length attribute for this tag. Maybe it is possible to control the length using the CSS. But it will effect all other buttons whoever used the same class id. Second, the onclick will trigger the event, it is not simply taken from html.
Take one button in standard for example, it shows
<a href="javascript:void(0)" class="th-bt th-bt-text-em" onclick="thBtMgr.click(this);return htmlbSL(this,2,'C3_W18_V19_V21_Search:search','0')" onmousedown="thBtMgr.press(this,event);" onfocusout="thBtMgr.unpress(this);" onfocus="thSaveKbFocus(this);" oncontextmenu="return false;" ondragstart="return false;" id="C3_W18_V19_V21_Search" title="Search Account"><span class="th-bt-span"><b class="th-bt-b">Search Account</b></span></a>
Here you may notice the event is not the simple event name.
Maybe you can think of using the image tag instead? So that you won't have the problem regarding length, and you can have CL_THTMLB_* class to generate the event for you?
Hongyan