$sExpReg = '';
 
   if( $sType == "CHAR" ){ $sExpReg = "/^[a-z]+$/i"; }         # CHAR = String
   elseif( $sType == "NUM" ){ $sExpReg = "/^[[:digit:]]+$/"; } # NUM  = Numbers
   elseif( $sType == "ALL" ){ $sExpReg = "/^[[:alnum:]]+$/"; } # ALL  = String and Numbers
   else{ return 0; }
 
   if( @preg_match( $sExpReg, $sString ) ){ return $sString; }
 }