+## ADD_HEADER(hdrs)
+##
+## An ACL action to add the given HDRS, which are a `\n'-terminated list of
+## new header lines.
+m4_define(<:ADD_HEADER:>, <:m4_dnl
+set acl_m_hdradd = ${if def:acl_m_hdradd{$acl_m_hdradd}{}}$1\n:>)
+
+## RENAME_HEADERS_ADD(list)
+##
+## Return a newline-separated list of message header additions of the form
+## X-Distorted-Renamed-HEADER: VALUE
+## for each HEADER in the LIST which appears in the current message, where
+## VALUE is the HEADER's current value.
+m4_define(<:RENAME_HEADERS_ADD:>, <:m4_dnl
+FOREACH(<:\
+ ${if def:h_$:><:1:{X-CONF_header_token-Renamed-$:><:1: $h_$:><:1:\n}}:>,
+ <:$1:>):>)
+
+## RENAME_HEADERS_REMOVE(list)
+##
+## Return the LIST, with items separated by colons.
+m4_define(<:RENAME_HEADERS_REMOVE:>, <:m4_dnl
+CLRSEP<::>FOREACH(<:SEP(:)$:><:1:>, <:$1:>):>)
+
+## WARNING_HEADER(tag, msg)
+##
+## Add a warning header to the current mesage.
+m4_define(<:WARNING_HEADER:>,
+<:add_header = X-CONF_header_token-Warning: $1 $2:>)
+