Thinking more deeply, I have changed the HTML.pm patch. The border property of the table element, if set to "1" (instead of ""), probably is best for HTML generation, and still produces a valid EPUB 3.3.
>From a6855aac641d78a781ed720cf070c2b5f07bc449 Mon Sep 17 00:00:00 2001 From: Daniel Cerqueira <dan....@lispclub.com> Date: Tue, 20 Aug 2024 21:51:19 +0100 Subject: [PATCH] tp/Texinfo/Convert/HTML.pm: Fix EPUB validity on table border - fix `epubchecker` error thrown on checking for validity of an EPUB file. This addresses the index <table ... border=...> element and property. Signed-off-by: Daniel Cerqueira <dan....@lispclub.com> --- tp/Texinfo/Convert/HTML.pm | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tp/Texinfo/Convert/HTML.pm b/tp/Texinfo/Convert/HTML.pm index 5901e0db53..81435076d9 100644 --- a/tp/Texinfo/Convert/HTML.pm +++ b/tp/Texinfo/Convert/HTML.pm @@ -5978,7 +5978,7 @@ sub _convert_printindex_command($$$$) # now format the index entries $result .= $self->html_attribute_class('table', ["$index_name-entries-$cmdname"]) - ." border=\"0\">\n" . '<tr><td></td>' + ." border=\"1\">\n" . '<tr><td></td>' . $self->html_attribute_class('th', ["entries-header-$cmdname"]).'>' # TRANSLATORS: index entries column header in index formatting . $self->convert_tree($self->gdt('Index Entry')) .'</th>' -- 2.45.2