code: function getBlockName(node, lookup, prefix) {
  	let depth = prefix.length > 1 ? prefix.length : 0;
  
  	// NB don’t walk up to root node, stay at first root child in case of
  	// too deep prefix
  	while (node.parent && node.parent.parent && depth--) {
  		node = node.parent;
  	}
  
  	return lookup.get(node) || '';
  }
docs: Returns block name for given `node` by `prefix`, which tells the depth of
  of parent node lookup
  @param  {Node} node
  @param  {Map} lookup
  @param  {String} prefix
  @return {String}