Alas, Exim is too old to understand this.
${if DKIM_SIGN_P \
{DKIM_KEYS_INSTANCE({${domain:$h_From:}})}}
dkim_selector = DKIM_KEYS_INFO(<:{KV(k)}:>)
${if DKIM_SIGN_P \
{DKIM_KEYS_INSTANCE({${domain:$h_From:}})}}
dkim_selector = DKIM_KEYS_INFO(<:{KV(k)}:>)
+ ##dkim_timestamps = m4_eval(<:7*24*60*60:>)
dkim_private_key = \
DKIM_KEYS_INSTANCE(<:m4_dnl
{CONF_dkim_keys_dir/$value/active/$dkim_selector.priv}:>)
dkim_private_key = \
DKIM_KEYS_INSTANCE(<:m4_dnl
{CONF_dkim_keys_dir/$value/active/$dkim_selector.priv}:>)