explain 'here-path better

pollen/private/ts.rktd

@@ -1 +1 @@
-1558741359
+1558981026

pollen/scribblings/command.scrbl

@@ -1,5 +1,5 @@
 #lang scribble/manual
-@(require scribble/bnf scribble/eval "utils.rkt" "mb-tools.rkt"
+@(require scribble/bnf scribble/eval "utils.rkt" "mb-tools.rkt" pollen/setup
           (for-syntax racket/base)
           (for-label rackunit pollen/core pollen/setup pollen/cache pollen/tag pollen/render pollen/template (only-in scribble/reader
                               use-at-readtable)))
@@ -612,7 +612,7 @@ Second, the metas are collected into a hash table that is exported with the name
 '#hasheq((dog . "Roxy") (cat . "Chopper") (here-path . "unsaved-editor"))
 }
 
-The only key that's automatically defined in every meta table is @id{'here-path}, which is the absolute path to the source file. (In this case, because the file hasn't been saved, you'll see the @val{unsaved-editor} name instead.) 
+The only key that's automatically defined in every meta table is @racket['#,(setup:here-path-key)], which is the absolute path to the source file. (In this case, because the file hasn't been saved, you'll see the @val{unsaved-editor} name instead.) 
 
 Still, you can override this too:
 

pollen/scribblings/core.scrbl

@@ -16,12 +16,17 @@ These functions are automatically imported into every Pollen source file (meanin
 
 @section{Metas}
 
+The only key that's automatically defined in every meta table is @racket['#,(setup:here-path-key)], which holds the absolute path to the source file. For instance, you could retrieve this value with @racket[(select-from-metas '#,(setup:here-path-key) metas)]. You can use something other than @racket['#,(setup:here-path-key)] as the key by overriding @racket[setup:here-path-key].
+
+For a full introduction to metas, see @secref["Inserting_metas"].
+
+
 @defform[(define-meta name value)]
 Add @racket[_value] to the metas of the current document, using @racket[_name] as the key.
 
 You can retrieve a meta value — even in the same document where you define it — with @racket[(select-from-metas _name metas)].
 
-For an introduction to metas, see @secref["Inserting_metas"].
+
 
 
 @section{Splicing}

pollen/scribblings/formats.scrbl

@@ -45,7 +45,7 @@ By default, every Pollen source file exports two identifiers:
 @itemlist[
 @item{@id{doc} contains the output of the file. The type of output depends on the source format (about which, more below).}
 
-@item{@id{metas} is a hashtable of key–value pairs with extra information that is extracted from the source. These @id{metas} will always contain the key @id{'here-path}, which returns a string representation of the full path to the source file. Beyond that, the only @id{metas} are the ones that are specified within the source file (see the source formats below for more detail on how to specify metas).}
+@item{@id{metas} is a hashtable of key–value pairs with extra information that is extracted from the source. These @id{metas} will always contain the key @racket['#,(setup:here-path-key)], which returns a string representation of the full path to the source file. Beyond that, the only @id{metas} are the ones that are specified within the source file (see the source formats below for more detail on how to specify metas).}
 ]
 
 As usual, you can use @racket[require], @racket[local-require], or @racket[dynamic-require] to retrieve these values. But within a Pollen project, the faster way is to use @racket[get-doc] and @racket[get-metas].

pollen/scribblings/setup.scrbl

@@ -159,6 +159,8 @@ If the cache can't find a certain file on the watchlist, no error will arise. Th
 
  @history[#:added "2.0"]}
 
+@defoverridable[here-path-key 'symbol]{Key used to store the path of the source file in its metas table. No idea why you'd want to change this.}
+
 
 @section{Parameters}