$ #create an array of tags and show all samples of the stamp <class />
$ cat a21.txt | perl -e '@a=<>; $"=""; $_="@a"; s/[\r\n]//g; @a=split/>/; foreach $_ (@a){if(/<class/) {s/^.*</</; s/$/>\n/; print;}}'
<class on=080705 from=overdue to=collect why=creditreform />
<class on=080705 from=overdue to=collect why=poursuites />
<class on=080716 from=billable to=fraud why=chargeback />
<class on=080625 from=billable to=overdue why=lost />
<class on=080625 from=billable to=overdue />
<class on=080829 from=shop to=billable why=contract />
<class on=080829 from=shop to=billable why=contract />
<class on=080716 from=billable to=fraud why=chargeback />
<class on=080705 from=overdue to=collect why=creditreform />
<class on=080625 from=billable to=overdue />
<class on=080705 from=overdue to=collect why=creditreform />
<class on=080625 from=billable to=overdue why=lost />

$ #retrieve the attributes
$ cat a21.txt | perl -e '@a=<>; $"=""; $_="@a"; s/[\r\n]//g; s/ ([a-z]+)=/ [$1]=/g; @a=split/\]/; foreach $_ (@a){if(/\[/) {s/^.*\[//; s/$/\n/; print;}}' | sort | uniq
from
on
to
what
why

$ #retrieve the stamps
$ cat a21.txt | perl -e '@a=<>; $"=""; $_="@a"; s/[\r\n]//g; @a=split/>/; foreach $_ (@a){if(/<[a-z]/) {/^.*<([a-z]+)/; $_=$1."\n"; print; }}' | sort | uniq
abuse
class
contract
found
identity
learn
limit
lost
remark
return
ship
supply
tariff
undue
until