Question about online WYSWYG editor

I JUST want to insert a WYSWYG editor  for customer to edit their fields in 'item list -new a inventry item'  

(i mean that add the WYSWYG editor in the netsuite system's item edit/new interface)

  how can i add a WYSWYG editor to a custom  item field 

  just like this  i type these word in the forum WYSWYG editor

it's very usefull  ....

   any one can help me  appreciate!!!!


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also I see  underside code in the netsuite system
<SPAN id='custitemcustitemaskitid_fs'><SCRIPT type='text/javascript'>
var editor = makeHtmlEditor('custitemcustitemaskitid',document.getElementById('custitemcustitemaskitid_fs_initValue').value,"this.isvalid=(nlapiValidateField(null,this));if (!this.isvalid) return false;this.isvalid=validate_textfield_maxlen(this,1000000,true,true);if (!this.isvalid) {getHtmlEditor('custitemcustitemaskitid').setFocus(); return false; }setWindowChanged(window, true);nlapiFieldChanged(null,this);",50,5, false, 0,null, null);