Content of beforeShowDay option

[ptkato]

In the docs, it's stated that through the use of the beforeShowDay option, it's possible to have custom content in place of the default value of day:

https://github.com/uxsolutions/bootstrap-datepicker/blob/fb8776d65825068b9f914ab37d6fd847c951f488/docs/options.rst?plain=1#L44

Now, what kind of content is accepted there? Is HTML accepted?