blogdown table of contents YAML

Hi, I'm wondering how HUGO can interpret the YAML for specifying a table of contents in blogdown. Typically in blogdown I specify a table of contents using this YAML:

    toc: true

In HUGO, it throws an error if you try to select this using eg: {{ if .Params.output.blogdown::html_page.toc }}, I think because the :: causes a parse error with HUGO. You can get rid of the error by using quotes, like `{{if .Param ".output.blogdown::html_page.toc" }}. But this doesn't seem to select anything. I'm not very experienced with YAML, so maybe I'm just using the wrong syntax to select that YAML parameter.