document support for multiple templates in ◊(define-meta template ...)

scribblings/render.scrbl

@@ -77,7 +77,18 @@ Note that @racket[_pagetree] or @racket[_pagetree_source] is used strictly as a
 Find a template file for @racket[_source-path], with the following priority:
 @itemlist[#:style 'ordered
 
-@item{If the @racket[metas] for @racket[_source-path] have a key for @code[(format "~a" world:template-meta-key)], then use the value of this key.}
+@item{If the @racket[metas] for @racket[_source-path] have a key for @code[(format "~a" world:template-meta-key)], then use the value of this key, e.g. —
+
+@code{◊(define-meta template "my-template.html")}
+
+If your project has @seclink["fourth-tutorial"]{multiple output targets}, you can supply a list of templates, and the template with an extension matching the current output target will be selected automatically, e.g. —
+
+@code{◊(define-meta template (list "my-template.html" "my-template.txt" "my-template.pdf"))}
+
+
+
+
+}
 
 @item{If this key doesn't exist, or refers to a nonexistent file, look for a default template with the name @code[(format "~a.[output extension]" world:default-template-prefix)]. Meaning, if @racket[_source-path] is @code[(format "intro.html.~a" world:markup-source-ext)], the output path would be @code["intro.html"], so the default template would be @code[(format "~a.html" world:default-template-prefix)]. Look for this default template in the same directory as the source file, and then search upwards within successive parent directories. (Corollary: a default template in the project root will apply to all files in the project unless overridden within a subdirectory.)}
 

scribblings/tutorial-fourth.scrbl

@@ -1,6 +1,6 @@
 #lang scribble/manual
 
-@(require scribble/eval racket/date (for-label racket/file racket/system pollen/decode plot pollen/world pollen/tag racket/base pollen/template txexpr racket/list racket/string))
+@(require scribble/eval racket/date (for-label racket/file racket/system pollen/decode plot pollen/world pollen/tag racket/base pollen/template txexpr racket/list racket/string pollen/render))
 @(require "mb-tools.rkt")
 
 @(define my-eval (make-base-eval))
@@ -200,7 +200,7 @@ The goal of this whole endeavor is to derive multiple output files from one sour
 ◊(apply string-append (filter string? (flatten doc)))
 }|]
 
-What we're doing here is converting the X-expression to text in a smarter way. We use @racket[local-require] to bring in @racket[racket/list] so we can use the @racket[flatten] function. Then, to understand what the next line does, just read it from the inside out: ``Take the @racket[doc] export from the source file (which is an X-expression), @racket[flatten] it into a list, @racket[filter] out everything that's not a @racket[string?] (creating a list that's only strings) and @racket[apply] the @racket[string-append] function to these, resulting in one big string.'' Which is exactly what we need for a plain-text file.
+What we're doing here is converting the X-expression to text in a smarter way. We use @racket[local-require] to bring in @racket[racket/list] so we can use the @racket[flatten] function. Then, to understand what the next line does, just read it from the inside out: ``Take the @racket[doc] export from the source file (which is an X-expression), @racket[flatten] it into a list, @racket[filter] with @racket[string?] (creating a list that's only strings) and @racket[apply] the @racket[string-append] function to these, resulting in one big string.'' Which is exactly what we need for a plain-text file.
 
 When you return to the project server and click on @filepath{cv.txt.pm}, you'll see the result:
 
@@ -211,6 +211,7 @@ Today is @(date->string (current-date)). I really want this job.}
 
 So far, so good. We've got legible plain text. But we've completely lost our formatting. Let's fix that.
 
+@margin-note{Have you ever used @code{◊(define-meta template ...)} to specify a  template for a particular source file? You can still use this in a multiple-output project — just supply a list of templates rather than a single template. See @racket[get-template-for].}
 
 @subsubsection{Branching tag functions}