HackMD
How to use tag list and tag filter
Tags are great for organizing your notes, and they shine when you are trying to locate one particular note – you have to tag each note in the first place, though.
You can filter through tags via tag list to the left pane of, or with the tag filter to the top of, the Overview page.
Tag List 
in the left pane
In the Overview of your Worksapce, click the downward caret to open the Tag List in the left pane.
There all tags that have been added to your notes in this Workspace will appear, with a number that counts how many notes include this tag.
Click the tag and the notes are filtered in the right pane.
Tip
Click tags while pressing Ctrl or Cmd to select multiple tags at once. Doing so will leave notes that include all selected tags only.
Tag Filter 
at the top of the Workspace
Clicking through Tag List is essentially selecting the tag in the Tag Filter, yet the latter has more superpowers!
- Select all: essentially the same as selecting all notes.
- 【AND】/【OR】: 【AND】selects notes that include all checked tags.【OR】selects notes that include any one of the checked tags.
- Search tag: filter tags with a keyword.
- Check or uncheck tags, and you will see the notes that have the checked tags listed below.
