CTasks::GetFilteredKeys

static function GetFilteredKeys($filter)
{
	$filteredKeys = [];

	if (is_array($filter))
	{
		foreach ($filter as $key => $value)
		{
			if ($key === '::LOGIC' || $key === '::MARKERS')
			{
				continue;
			}

			if (static::isSubFilterKey($key))
			{
				$filteredKeys = array_merge($filteredKeys, self::GetFilteredKeys($value));
				continue;
			}

			$operationFilter = CTasks::MkOperationFilter($key);
			$operationField = $operationFilter['FIELD'];

			if ($operationField !== '')
			{
				$filteredKeys[] = mb_strtoupper($operationField);
			}
		}
	}

	return array_unique($filteredKeys);
}