What is the node:id cache tag equivalent for blocks? I am wondering why the last two entries do not work:

public function getCacheTags() {
  $tags = [
    'node:270',
    'node:271',
    'node:273',
    'node:282',
    'block:customblockname',
    'block:7',
  ];
  $cacheTags = Cache::mergeTags(parent::getCacheTags(), $tags);

  return $cacheTags;
}


When I edit my custom block the URL is:


  /block/7?destination=/admin/structure/block/block-content


The actual id of the block (for instance when embedding it) is customblockname.

What are the correct cache tags to include that block in my caching?
I just figured myself. The cache tag for custom blocks is simply:

block_content:7