@defparam[current-metas val (or/c #f hash?) #:value #f]
Holds the @racket[metas] of the current Pollen source. In tag functions, rather than pass @racket[metas] as an argument, you can refer to @racket[(current-metas)] within the body of the function. Likewise, if your tag function calls other tag functions, they can all invoke @racket[(current-metas)] instead of passing the value around.
@racket[(current-metas)] will also work in templates, holding the @racket[metas] of the source currently being rendered into the template.
