bkmTagsByID implements sorting by the last tag item ID

Taggable leaf policy when tags structure changes: either keep the taggings of the new leaf, or delete it

Either ID or Username should be given.

Implements storage.Storage

TODO: find a better name

TaggingMode is used for GetTaggings(), SetTaggings: specifies whether given argument/returned value should contain all tags (including all supertags),

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Tags tree cache {{{

TagPather impl {{{

NOTE: perUserTestFunc shoult NOT take *testing.T argument, because this function should be able to run in parallel with others, and testing.T is not d

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taghier's registry implementation which hits the database {{{

Hierarchy is as follows: ├── 1 │   ├── 4 │   │   └── 7 │   │   └── 8 │   ├── 5 │   │   └── 9 │   └── 6 │   └── 10 │   ├── 11 │