Index: code-docs/dust.scrbl
==================================================================
--- code-docs/dust.scrbl
+++ code-docs/dust.scrbl
@@ -155,10 +155,24 @@
 
 @defproc[(series-title) string?]
 
 If @code{(current-metas)} has the key @racket['series], and if the corresponding series defines a meta
 value for @racket['title], then return it, otherwise return @racket[""].
+
+@defproc[(invalidate-series) (or/c void? boolean?)]
+
+If the current article specifies a @racket['series] meta, and if a corresponding @filepath{.poly.pm}
+file exists in @racket[series-folder], attempts to “touch” the last-modified timestamp on that file,
+returning @racket[#t] on success or @racket[#f] on failure. If either precondition is not true,
+returns @|void-const|.
+
+When an article is being rendered, that means the article has changed, and if the article has
+changed, its series page (if any) should be updated as well. Touching the @filepath{.poly.pm} file
+for a series page triggers a re-render of that page when running @tt{make web} to rebuild the web
+content (see @repo-file{makefile}).
+
+Only used in one place, @repo-file{tags-html.rkt}.
 
 @defproc[(disposition-values [str string?]) any]
 
 Given a string @racket[_str], returns two values: the portion of the string coming before the first
 space, and the rest of the string.