Q:

Ignore capital and small initial letters

I would like to set that the use of capital and small initial letters should be ignored in this search script. So if I write "hello" or "HEllo" ... it should bring the same results.
Here is the script:
<input type="text" class="boxformal boxformal-cf" placeholder="Diese Seite durchsuchen ..." onkeyup="
for( var elms=document.getElementById('content')
                      .getElementsByTagName('article')
     ,      L=elms.length
   ; L--
   ; elms[L].className= ~elms[L].textContent.indexOf(this.value)
                      ? found='searchopt kurse-standart standart-grau groesse-15'
                      : 'donotshow'
   );
   this.nextSibling.innerHTML= found ? '' : 'Es wurde nichts gefunden!' ;
">

Thank you for helping!
P.s.: Some phrases are in German :)

A:

what about changing the casing of the strings?
<input type="text" class="boxformal boxformal-cf" placeholder="Diese Seite durchsuchen ..." onkeyup="
for( var elms=document.getElementById('content')
                      .getElementsByTagName('article')
     ,      L=elms.length
   ; L--
   ; elms[L].className= ~elms[L].textContent.toLowerCase().indexOf(this.value.toLowerCase())
                      ? found='searchopt kurse-standart standart-grau groesse-15'
                      : 'donotshow'
   );
   this.nextSibling.innerHTML= found ? '' : 'Es wurde nichts gefunden!' ;
">

