Google shows you search results while you typing text in search box. I made same function in roundcube search box by editing in
\program\include\rcmail_output_html.php
Lines:
1930: array('id','class','style','name','method','action','enctype','onsubmit')
2168: 'onsubmit' => sprintf("%s.command('%s'); return false", self::JS_OBJECT_NAME, $attrib['command'] ?: 'search'),
to
1930: array('id','class','style','name','method','action','enctype','onsubmit','oninput')
2168:'oninput' => sprintf("%s.command('%s'); return false", self::JS_OBJECT_NAME, $attrib['command'] ?: 'search'),
I thing if developers add additional option to setting, that will enable/disable such option - will be great)