Nested if/else tags can become very ugly... Fortunately ACS comes with an elseif tag! Unfortunately it's broken...
In acs-templating/tcl/tag-procs.tcl, change line 52 from:
append condition "} {"
template::adp_append_code $condition
to
append condition "} {"
switch $condition_type {
if {template::adp_append_code $condition}
elseif {template::adp_append_code $condition -nobreak}
}