code: public static function setGet($strKey, $varValue, $blnAddUnused=false)
  	{
  		// Convert special characters (see #7829)
  		$strKey = str_replace(array(' ', '.', '['), '_', $strKey);
  
  		$strKey = static::cleanKey($strKey);
  
  		unset(static::$arrCache['getEncoded'][$strKey]);
  		unset(static::$arrCache['getDecoded'][$strKey]);
  
  		if ($varValue === null)
  		{
  			unset($_GET[$strKey]);
  		}
  		else
  		{
  			$_GET[$strKey] = $varValue;
  
  			if ($blnAddUnused)
  			{
  				static::setUnusedGet($strKey, $varValue); // see #4277
  			}
  		}
  	}
docs: Set a $_GET variable
  
  @param string  $strKey       The variable name
  @param mixed   $varValue     The variable value
  @param boolean $blnAddUnused If true, the value usage will be checked