◊(Local Yarn Code "Diff")

If @code{(current-metas)} has the key @racket['series], and if the corresponding series defines a meta
value for @racket['noun-singular], then return it, otherwise return @racket[""].

@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.

@examples[#:eval dust-eval