_bem_context = {
	_alias_map: {}
	_alias_stack: () ()
}
			
work_stack(stack, callback)
	while length(stack) > 0
		entry = pop(stack)
		if entry != ()
			callback(entry)

set_alias(alias, name)
	if name != null && alias != null
		_bem_context._alias_map[alias] = name
	
lookup_alias(name)
	if name in _bem_context._alias_map
		return _bem_context._alias_map[name]
	else
		return name

store_alias(alias)
	if alias != null
		push(_bem_context._alias_stack, alias)
	
pop_last_alias()
	return pop(_bem_context._alias_stack)
	
apply_alias_stack(name)
	work_stack(_bem_context._alias_stack, @(element){
		set_alias(element, name)
	})

auto_name(delimiter)
	if length(called-from) < 3
		return null
	name = split(delimiter, called-from[2])[-1]
	if name in ('RV-Element' 'RV-Block' 'RV-Element--modifier' 'RV-Block--modifier')
		return null
	return name

is_nested(mixin_name=null)
	_free_hits = 0
	if mixin_name == null
		shift(called-from)
		mixin_name = shift(called-from)
	else 
		_free_hits = 1
	for parent in called-from
		if parent == mixin_name
			if _free_hits == 0
				return true
			else
				_free_hits = _free_hits - 1
	return false

is_nested_in(parent_name)
	return parent_name in called-from
	
not_nested_in(parent_name)
	return !(parent_name in called-from)

RV-Level(name, name_delimiter, allowed_parent_levels, selector_callback)
	if name == null
		name = auto_name(name_delimiter)
	not_in_parent = true
	for parent_level in allowed_parent_levels
		not_in_parent = not_in_parent && not_nested_in(parent_level)
	if is_nested_in('RV-Squash') || not_in_parent
		{block}
	else if is_nested()
		store_alias(name)
		{block}
	else
		if name == null
			name = pop_last_alias()
		name = lookup_alias(name)
		apply_alias_stack(name)
		
		{selector_callback(name)}
			{block}



RV-Block(name)
	.{name}
		+prefix-classes(name)
			{block}
	
	_bem_context._alias_map = {}
	_bem_context._alias_stack = () ()
		
RV-Element(name=null)
	+RV-Level(name, '__', ('RV-Block' 'RV-Block--modifier'), @(name){
		if is_nested_in('RV-Block--modifier') {
			return '& .__' + name
		}
		else {
			return '&__' + name
		}
	})
		{block}
		
		
RV-Element--modifier(name=null)
	+RV-Level(name, '--', ('RV-Element'), @(name){return '&--' + name})
		{block}
		
RV-Block--modifier(name=null)
	+RV-Level(name, '--', ('RV-Block'), @(name){return '&--' + name})
		{block}
		
RV-Squash()
	{block}