?repeats the group contents below at most once:
\s*?any whitespace character, repeated any number of times
dethe literal text de (case insensitive) \s*?any whitespace character, repeated any number of times
\d{1,2}a digit, repeated between 1 and 2 times
\s*?any whitespace character, repeated any number of times
dethe literal text de (case insensitive) \s*any whitespace character, repeated any number of times
Group 12(janeiro|fevereiro|março|abril|maio|junho|julho|agosto|setembro|outubro|novembro|dezembro) \s*?any whitespace character, repeated any number of times
dethe literal text de (case insensitive) \s*?any whitespace character, repeated any number of times
\d{2,4}a digit, repeated between 2 and 4 times