confusing context string 'F', 'Month long name'

report3 & report4 files have :

return _(zbx_date2str(_x('F', 'Month long name'), $t));

in pootle it looks like this :
https://www.zabbix.org/pootle/pt_BR/Zabbix-trunk/translate.html#unit=394139

in such context astrings we should say that it's php date/time format string etc

we should also list this in one of the guideline pages