Hi Vivek,
This is hard coded, you cannot change it. This is done by following method. You can check and
modify if you want more.
CL_THTMLB_F4HELP Method
IF_CRM_WEB_CALLBACK~HANDLE_REQUEST
I also provide you following SAP Help link for your reference. Using the Smart Input Help: http://help.sap.com/saphelp_crm70/helpdata/en/80/d1fe7d1c814eeda259e30923ce3f63/frameset.htm
Best Regards, Bruce