Tags are a means to group Objects in meaningful ways. In concept they are similar to “classes”, “types” or “tables.”

There are a few types of tags:

#Root tags: every object has a root tag — mapping to what kind of markdown object was tagged, e.g. page, task, paragraph, or item.
#User tags: optionally, an object can receive one or more user tags that are explicitly attached, either via the tags frontmatter attribute, or by using a Markdown/Hashtags in markdown.
#Edge tags: specically: Tag/relation whose objects are automatically derived from links that appear in a page.

Confused? Start with Guide/Add Structure and Query for some examples.

Root tags

A root tag maps an object to a Markdown element or a file. Every root tag also accepts user tags.

data: Objects defined in fenced YAML data blocks.
document: Every non-Markdown file in your space: images, PDFs, attachments.
header: Markdown headings.
item: Bullet and numbered list items.
page: Every page in your space.
paragraph: Top-level paragraphs that carry a hashtag or anchor.
table: Rows of Markdown tables.
task: Checkbox list items, including their completion state.

You can also define root tags of your own, using a fenced data block with a hashtag as its language:

```#contact
name: Sam Rivera
```

User tags

User tags are created implicitly when you use the Markdown/Hashtags syntax, or list them in the tags attribute of Frontmatter or a data block. They are attached to an object in addition to its root tag: a task tagged #upnext has root tag task and user tag upnext, and is returned both by index.tasks() and index.objects("upnext").

You can extend the behavior of any tag, root or user, via the API/tag API, for instance to give it a Schema.

Edge tags

Objects are the nodes of the Graph View. Edges connect them.

relation: Connections between objects: links, mentions and typed attributes.

System tags

These are used, mostly for internal use to store markdown blocks that configure SilverBullet rather than hold content. You can’t attach tags to them, and commenting one out turns it off.

space-lua: Space Lua code blocks, run when the client boots.
space-style: Space Style CSS blocks, applied to the client.

Index tags

Records the Object Index keeps about the space itself. They are computed, with no Markdown of their own.

ambiguous-link: Links whose name matches more than one page.
anchor: Named anchors, each pointing at the object it is attached to.
aspiring-page: Pages that are linked to but do not exist yet.
identity: The @name mentions across the space.
tag: Every tag used in the space, with the root tag it is used on.