These can be used in text to assign a Tag. If hashtags are the only content of the first paragraph, they are applied to the entire page.

Hashtags can contain letters, dashes, underscores and other characters, but not: - Whitespace (space, newline, etc.) - Characters from this list: !@#$%^&*(),.?":{}|<>\ - Digits only (e.g. #123)

If you need your tags to contain these characters, you have to surround the tag content with angle brackets like this: #