Files in Hyperdrive can have metadata values.
Metadata is stored as a UTF-8 string. Each value is identified by a key string. You can put as many metadata values as you like on a file, but avoid going too far or you'll slow down reads.
In the editor
Visit the file you want to modify and open the editor. Then click on the "File Metadata" button on the toolbar.
A dropdown will appear with the metadata keys on the left and the values on the right. Use the empty inputs on the bottom to add a new value. You can modify existing values or remove them by simply deleting their values.
When you are finished, click "Save" to write the changes.