Preview switches

[Q. Schroll]

Entering dmd -preview=h shows this list:

   =all              list information on all upcoming language 
changes
   =dip25            implement [..] (Sealed references)
   =dip1000          implement [..] (Scoped Pointers)
   =dip1008          implement [..] (@nogc Throwable)
   =dip1021          implement [..] (Mutable function arguments)
   =fieldwise        use fieldwise comparisons for struct equality
   =markdown         enable Markdown replacements in Ddoc
   =fixAliasThis     when a symbol is resolved, check alias this 
scope before going to upper scopes
   =intpromote       fix integral promotions for unary + - ~ 
operators
   =dtorfields       destruct fields of partially constructed 
objects
   =rvaluerefparam   enable rvalue arguments to ref parameters
   =nosharedaccess   disable access to shared memory objects
   =in               in means scope const

While "implement <DIP link omitted>" do link to documents 
explaining details, I have no idea what `rvaluerefparam` does 
exactly. Is there an (online) resource where details to the 
others are given or linked?