This was described when Beta 1.7f-3 was distributed. Not sure if it ever
made the release notes. Here is the relevant prose from Eric:
An optional "digest header" text can be inserted between the end of the
table of contents and the beginning of the digest itself. If a LISTSERV
(not CMS) file by the name 'listname DIGEST-H' is found, its contents
will be inserted at this point in the digest. This file, like list
welcome messages, can be maintained by the list owner.
The instructions and job skeleton at the end of indexes can be replaced
(not added to) by shorter, customized text from the file 'listname
INDEX-H'. Again, if that file exists it replaces EVERYTHING after the
list of messages. If you want the instructions to remain, just copy them
to the INDEX-H file. The purpose of this addition is to replace the
instructions with a version better tailored to your audience (no point
explaining about REPLY TEXT if your audience is 100% PROFS).