sed or perl pattern match and then multiple actions - sed

Question

I want to search for a variable numeric value at the end of a line, once found, do two things:
append something to the end of that line (for example, an html tag)
move down as many line as that numeric value and append a line there as well (for example, close the preceding html tag).
Any quick pointers please? Attached is a screenshot of my sample data and desired changes. Note in some cases, if there is no member, there won't be any numeric value at the end of the line.
Sample data

Answer 1

Your data is in well structure. It is totally fine to use sed.
You need to identify the headers, then operate on them.
input
header 1
item 1.1
item 1.2
item 1.3
header 2
item 2.1
item 2.2
item 2.3
header 3
item 3.1
item 3.2
item 3.3
command
sed -r '/^\S/{s#$#<wrap>#; 1!s#^#</wrap>\n#}; $s#$#</wrap>#' input
output
header 1<wrap>
item 1.1
item 1.2
item 1.3
</wrap>
header 2<wrap>
item 2.1
item 2.2
item 2.3
</wrap>
header 3<wrap>
item 3.1
item 3.2
item 3.3
</wrap>

Answer 2

OK, I guess I'll settle with this one liner for now (see my sample data in the question):
perl -pe '/\((\d+) members?\)/ && do {$close = $.+$1; s/$/OPEN_TAG/;}; $.==$close && do {s/$/CLOSE_TAG/};' input-file