Hi there,
baseof works with taxonomy/tag.html for me.
Please have a read about Requesting Help to see how to ask for help.
We need to be able to replicate your issue to be able to help you. Snippets are not usually very useful unless accompanied by site context. As for screenshots, whenever I see someone here post a question accompanied by one, my immediate assumption (and likely that of others’ as well) is that the poster is a newbie and also respond accordingly, usually with links to tutorials like the above.
As for example code, there’s plenty of baseof in the wild in the Themes section.