Add W3C validator script

Makefile

@@ -27,3 +27,6 @@ img/sprites.png: $(sprites)
 css/sprites.css: img/sprites.png xquery/build_sprites_css.xqy
 	xidel --extract-kind=xquery3 --extract-file=xquery/build_sprites_css.xqy > $@
 	chmod a+r $@
+
+validate: feed.xml
+	xidel --extract-kind=xquery3 --extract-file=xquery/validator.xqy

xquery/validator.xqy

@@ -0,0 +1,45 @@
+declare namespace m = "http://www.w3.org/2005/10/feed-validator";
+
+parse-xml(x:request(x:form(
+  <form action="https://validator.w3.org/feed/check.cgi">
+    <input name="output" value="soap12" />
+    <input name="url" value="https://envs.net/~lucidiot/rsrsss/feed.xml" />
+  </form>
+))/raw)//m:feedvalidationresponse ! concat(
+  "W3C feed validation results for ",
+  m:uri,
+  " on ",
+  m:date,
+  ": ",
+  switch (m:validity)
+    case "true" return "VALID"
+    case "false" return "INVALID"
+    default return concat("UNKNOWN (", ., ")"),
+  "&#10;",
+  m:errors/m:errorcount,
+  " errors, ",
+  m:warnings/m:warningcount,
+  " warnings, ",
+  m:informations/m:infocount,
+  " informations&#10;",
+  string-join((
+    m:errors/m:errorlist/error,
+    m:warnings/m:warninglist/warning,
+    m:informations/m:infolist/info
+  ) ! concat(
+    "&#10;",
+    upper-case(name()),
+    " at line ",
+    if (backupline ne line) then backupline else line,
+    ", column ",
+    if (backupcolumn ne column) then backupcolumn else column,
+    ": ",
+    text,
+    if (number(msgcount) gt 1) then concat("&#10;  Repeated ", msgcount, "times") else "",
+    "&#10;  Documentation: https://validator.w3.org/feed/docs/",
+    lower-case(name()),
+    "/",
+    type,
+    ".html"
+  ), "&#10;")
+)