Found under: Settings > Song Actions > Song tags
Tags can be used to group songs into various categories, themes, song books, etc. In the desktop version of OpenSong, tags are referred to as 'themes'.
You can edit individual song tags from the Edit song page, but if you wish to bulk assign tags to multiple songs at once, you should use this option instead.
When displaying songs in the song index, filter by tags is the furthest right option at the top of the screen.
Use the filter buttons at the top to filter which songs you wish to manage the tags for (by title, content search, key, author/artist, folder, tag)
Select the tag you want to add or remove from songs from the drop down list (you can also add new tags using the + button).
To only show songs containing this tag, click on the filter button to the right of the chosen tag. Clicking this a second time will remove this filter.
Clicking on any song that is highlighted will remove the chosen tag and clicking on songs that are not highlighted will add the chosen tag to that song.
When editing a song via the Edit song page, you can assign an existing tag to the song.
If you want to add a new tag, expand the popup window, or scroll down and enter a new song tag name.
Checking or unchecking a song tag item will add or remove that tag from the existing song.
Clicking on the trash icon will remove that tag from all matching song, effectively removing the tag. You will be asked to confirm this action before proceeding.