analysis of how autofile and autoindex differ

doc/todo/autoindex_should_use_add__95__autofile.mdwn

@@ -15,6 +15,8 @@ quite, entirely unlike". I tried digging through the git history for the
 reasoning behind the autofile and autoindex implementations, but now I'm
 mostly confused.
 
+## autofile
+
 The autofile machinery records a list of every file that has ever been proposed
 as an autofile: for instance, the tag plugin has a list of every tag that
 has ever been named in a \[[!tag]] or \[[!taglink]], even if no file was
@@ -23,11 +25,74 @@ already exist (or whatever) are deferred until after this list has been
 updated, and files in this list are never auto-created again unless the wiki
 is rebuilt.
 
+This avoids re-creating the tag `create-del` in this situation, which is
+the third one that I noted on
+[[todo/auto-create tag pages according to a template]]:
+
+* create tags/create-del manually
+* tag a page as create-del
+* delete tags/create-del
+
+and also avoids re-creating `auto-del` in this similar situation (which I
+think is probably the most important one to get right):
+
+* tag a page as auto-del, which is created automatically
+* delete tags/auto-del
+
+I think both of these are desirable.
+
+However, this infrastructure also results in the tag page not being
+re-created in either of these situations (the first and second that I noted
+on the other page):
+
+* tag a page as auto-del-create-del, which is created automatically
+* delete tags/auto-del-create-del
+* create tags/auto-del-create-del manually
+* delete tags/auto-del-create-del again
+
+or
+
+* create tags/create-del-auto
+* delete tags/create-del-auto
+* tag a page as create-del-auto
+
+I'm less sure that these shouldn't create the tag page: we deleted the
+manually-created version, but that doesn't necessarily mean we don't want
+*something* to exist.
+
+## autoindex
+
 The autoindex machinery records a more complex set. Items are added to the
 set when they are deleted, but would otherwise have been added as an autoindex
 (don't exist, do have children (by which I mean subpages or attachments),
 and are a directory in the srcdir). They're removed if this particular run
 wouldn't have added them as an autoindex (they exist, or don't have children).
 
-Still researching why there's this difference, and whether one or the other
+Here's what happens in situations mirroring those above.
-would be better for all cases...
+
+The "create-del" case still doesn't create the page:
+
+* create create-del manually
+* create create-del/child
+* delete create-del
+* it's added to `%deleted` and not re-created
+
+Neither does the "auto-del" case:
+
+* create auto-del/child, resulting in auto-del being created automatically
+* delete auto-del
+* it's added to `%deleted` and not re-created
+
+However, unlike the generic autofile infrastructure, `autoindex` forgets
+that it shouldn't re-create the deleted page in the latter two situations:
+
+* create auto-del-create-del/child, resulting in auto-del-create-del being
+  created automatically
+* delete auto-del-create-del; it's added to `%deleted` and not re-created
+* create auto-del-create-del manually; it's removed from `%deleted`
+* delete auto-del-create-del again (it's re-created)
+
+* create create-del-auto
+* delete create-del-auto; it's not added to `%deleted` because there's no
+  child that would cause it to exist
+* create create-del-auto/child