PPX rewriter help

Learning
1

in constructing an extension with

let blah =
  Extension.declare
    "blah"
    Extension.Context.structure_item
    Ast_pattern.(pstr (pstr_value __ ((value_binding ~pat:( __) ~expr:__ ) ^:: nil) ^::nil)) 
...

how should the next line look in equivalent metaquot?
I have tried all sorts, like (nonrec flag capture omitted):

  [%stri let [%p __] = [%e __] ]
and
  [%stri let [%p __] = [%e __] ]
and
  [%stri let [%p? __] = [%e? __] ]
and
  [%stri? let [%p __] = [%e __] ]
and
  [%stri? let [%p? __] = [%e? __] ]
and
  [%stri let __ = __ ]
and
  [%stri let _ = _ ]
and
...

but the right way is elusive.
I’d like to capture the nonrec flag also as per the combinator line.
do the comments of ast_pattern.mli and ppx-for-plugin-authors.rst constitute the whole documentation?